[PATCH] MM: introduce memalloc_retry_wait()

[PATCH] MM: introduce memalloc_retry_wait()

[NeilBrown]

Various places in the kernel - largely in filesystems - respond to a
memory allocation failure by looping around and re-trying.
Some of these cannot conveniently use __GFP_NOFAIL, for reasons such as:
 - a GFP_ATOMIC allocation, which __GFP_NOFAIL doesn't work on
 - a need to check for the process being signalled between failures
 - the possibility that other recovery actions could be performed
 - the allocation is quite deep in support code, and passing down an
   extra flag to say if __GFP_NOFAIL is wanted would be clumsy.

Many of these currently use congestion_wait() which (in almost all
cases) simply waits the given timeout - congestion isn't tracked for
most devices.

It isn't clear what the best delay is for loops, but it is clear that
the various filesystems shouldn't be responsible for choosing a timeout.

This patch introduces memalloc_retry_wait() with takes on that
responsibility.  Code that wants to retry a memory allocation can call
this function passing the GFP flags that were used.  It will wait
however is appropriate.

For now, it only considers the __GFP_DIRECT_RECLAIM and __GFP_NORETRY
flags.  If DIRECT_RECLAIM is set without GFP_NORETRY, then alloc_page
either made some reclaim progress, or waited for a while, before
failing.  So there is no need for much further waiting.
memalloc_retry_wait() will wait until the current jiffie ends.  If this
condition is not met, then alloc_page() won't have waited.  In that case
memalloc_retry_wait() waits about 200ms.  This is the delay that most
current loops uses.

linux/sched/mm.h needs to be included in some files now,
but linux/backing-dev.h does not.

Signed-off-by: NeilBrown <neilb@suse.de>
---

I could split this up by filesystems if people prefer that, but they we
would have to wait for the -mm patch to land before they could be
applied.  What do people think?  Can Andrew just collected acked-bys?

Thanks,
NeilBrown


 fs/ext4/extents.c        |  8 +++-----
 fs/ext4/inline.c         |  5 ++---
 fs/ext4/page-io.c        |  9 +++++----
 fs/f2fs/data.c           |  3 +--
 fs/f2fs/gc.c             |  5 ++---
 fs/f2fs/inode.c          |  4 ++--
 fs/f2fs/node.c           |  3 +--
 fs/f2fs/recovery.c       |  6 +++---
 fs/f2fs/segment.c        |  8 ++------
 fs/f2fs/super.c          |  4 +---
 fs/xfs/kmem.c            |  3 +--
 fs/xfs/xfs_buf.c         |  2 +-
 include/linux/sched/mm.h | 21 +++++++++++++++++++++
 net/sunrpc/svc_xprt.c    |  2 +-
 14 files changed, 46 insertions(+), 37 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 0ecf819bf189..5582fba36b44 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -27,8 +27,8 @@
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 #include <linux/fiemap.h>
-#include <linux/backing-dev.h>
 #include <linux/iomap.h>
+#include <linux/sched/mm.h>
 #include "ext4_jbd2.h"
 #include "ext4_extents.h"
 #include "xattr.h"
@@ -4407,8 +4407,7 @@ int ext4_ext_truncate(handle_t *handle, struct inode *inode)
 	err = ext4_es_remove_extent(inode, last_block,
 				    EXT_MAX_BLOCKS - last_block);
 	if (err == -ENOMEM) {
-		cond_resched();
-		congestion_wait(BLK_RW_ASYNC, HZ/50);
+		memalloc_retry_wait(GFP_ATOMIC);
 		goto retry;
 	}
 	if (err)
@@ -4416,8 +4415,7 @@ int ext4_ext_truncate(handle_t *handle, struct inode *inode)
 retry_remove_space:
 	err = ext4_ext_remove_space(inode, last_block, EXT_MAX_BLOCKS - 1);
 	if (err == -ENOMEM) {
-		cond_resched();
-		congestion_wait(BLK_RW_ASYNC, HZ/50);
+		memalloc_retry_wait(GFP_ATOMIC);
 		goto retry_remove_space;
 	}
 	return err;
diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 39a1ab129fdc..635bcf68a67e 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -7,7 +7,7 @@
 #include <linux/iomap.h>
 #include <linux/fiemap.h>
 #include <linux/iversion.h>
-#include <linux/backing-dev.h>
+#include <linux/sched/mm.h>
 
 #include "ext4_jbd2.h"
 #include "ext4.h"
@@ -1929,8 +1929,7 @@ int ext4_inline_data_truncate(struct inode *inode, int *has_inline)
 retry:
 			err = ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
 			if (err == -ENOMEM) {
-				cond_resched();
-				congestion_wait(BLK_RW_ASYNC, HZ/50);
+				memalloc_retry_wait(GFP_ATOMIC);
 				goto retry;
 			}
 			if (err)
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 9cb261714991..1d370364230e 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -24,7 +24,7 @@
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/mm.h>
-#include <linux/backing-dev.h>
+#include <linux/sched/mm.h>
 
 #include "ext4_jbd2.h"
 #include "xattr.h"
@@ -523,12 +523,13 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 			ret = PTR_ERR(bounce_page);
 			if (ret == -ENOMEM &&
 			    (io->io_bio || wbc->sync_mode == WB_SYNC_ALL)) {
-				gfp_flags = GFP_NOFS;
+				gfp_t new_gfp_flags = GFP_NOFS;
 				if (io->io_bio)
 					ext4_io_submit(io);
 				else
-					gfp_flags |= __GFP_NOFAIL;
-				congestion_wait(BLK_RW_ASYNC, HZ/50);
+					new_gfp_flags |= __GFP_NOFAIL;
+				memalloc_retry_wait(gfp_flags);
+				gfp_flags = new_gfp_flags;
 				goto retry_encrypt;
 			}
 
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 9f754aaef558..48b80e7ec35e 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -10,7 +10,6 @@
 #include <linux/buffer_head.h>
 #include <linux/mpage.h>
 #include <linux/writeback.h>
-#include <linux/backing-dev.h>
 #include <linux/pagevec.h>
 #include <linux/blkdev.h>
 #include <linux/bio.h>
@@ -2542,7 +2541,7 @@ int f2fs_encrypt_one_page(struct f2fs_io_info *fio)
 		/* flush pending IOs and wait for a while in the ENOMEM case */
 		if (PTR_ERR(fio->encrypted_page) == -ENOMEM) {
 			f2fs_flush_merged_writes(fio->sbi);
-			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+			memalloc_retry_wait(GFP_NOFS);
 			gfp_flags |= __GFP_NOFAIL;
 			goto retry_encrypt;
 		}
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index a946ce0ead34..374bbb5294d9 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -7,7 +7,6 @@
  */
 #include <linux/fs.h>
 #include <linux/module.h>
-#include <linux/backing-dev.h>
 #include <linux/init.h>
 #include <linux/f2fs_fs.h>
 #include <linux/kthread.h>
@@ -15,6 +14,7 @@
 #include <linux/freezer.h>
 #include <linux/sched/signal.h>
 #include <linux/random.h>
+#include <linux/sched/mm.h>
 
 #include "f2fs.h"
 #include "node.h"
@@ -1375,8 +1375,7 @@ static int move_data_page(struct inode *inode, block_t bidx, int gc_type,
 		if (err) {
 			clear_page_private_gcing(page);
 			if (err == -ENOMEM) {
-				congestion_wait(BLK_RW_ASYNC,
-						DEFAULT_IO_TIMEOUT);
+				memalloc_retry_wait(GFP_NOFS);
 				goto retry;
 			}
 			if (is_dirty)
diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 0f8b2df3e1e0..4c11254a07d4 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -8,8 +8,8 @@
 #include <linux/fs.h>
 #include <linux/f2fs_fs.h>
 #include <linux/buffer_head.h>
-#include <linux/backing-dev.h>
 #include <linux/writeback.h>
+#include <linux/sched/mm.h>
 
 #include "f2fs.h"
 #include "node.h"
@@ -562,7 +562,7 @@ struct inode *f2fs_iget_retry(struct super_block *sb, unsigned long ino)
 	inode = f2fs_iget(sb, ino);
 	if (IS_ERR(inode)) {
 		if (PTR_ERR(inode) == -ENOMEM) {
-			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+			memalloc_retry_wait(GFP_NOFS);
 			goto retry;
 		}
 	}
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 556fcd8457f3..f8646c29e00b 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -8,7 +8,6 @@
 #include <linux/fs.h>
 #include <linux/f2fs_fs.h>
 #include <linux/mpage.h>
-#include <linux/backing-dev.h>
 #include <linux/blkdev.h>
 #include <linux/pagevec.h>
 #include <linux/swap.h>
@@ -2750,7 +2749,7 @@ int f2fs_recover_inode_page(struct f2fs_sb_info *sbi, struct page *page)
 retry:
 	ipage = f2fs_grab_cache_page(NODE_MAPPING(sbi), ino, false);
 	if (!ipage) {
-		congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+		memalloc_retry_wait(GFP_NOFS);
 		goto retry;
 	}
 
diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c
index 6a1b4668d933..d1664a0567ef 100644
--- a/fs/f2fs/recovery.c
+++ b/fs/f2fs/recovery.c
@@ -8,6 +8,7 @@
 #include <asm/unaligned.h>
 #include <linux/fs.h>
 #include <linux/f2fs_fs.h>
+#include <linux/sched/mm.h>
 #include "f2fs.h"
 #include "node.h"
 #include "segment.h"
@@ -587,7 +588,7 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,
 	err = f2fs_get_dnode_of_data(&dn, start, ALLOC_NODE);
 	if (err) {
 		if (err == -ENOMEM) {
-			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+			memalloc_retry_wait(GFP_NOFS);
 			goto retry_dn;
 		}
 		goto out;
@@ -670,8 +671,7 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,
 			err = check_index_in_prev_nodes(sbi, dest, &dn);
 			if (err) {
 				if (err == -ENOMEM) {
-					congestion_wait(BLK_RW_ASYNC,
-							DEFAULT_IO_TIMEOUT);
+					memalloc_retry_wait(GFP_NOFS);
 					goto retry_prev;
 				}
 				goto err;
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index df9ed75f0b7a..6140eada8607 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -245,9 +245,7 @@ static int __revoke_inmem_pages(struct inode *inode,
 								LOOKUP_NODE);
 			if (err) {
 				if (err == -ENOMEM) {
-					congestion_wait(BLK_RW_ASYNC,
-							DEFAULT_IO_TIMEOUT);
-					cond_resched();
+					memalloc_retry_wait(GFP_NOFS);
 					goto retry;
 				}
 				err = -EAGAIN;
@@ -424,9 +422,7 @@ static int __f2fs_commit_inmem_pages(struct inode *inode)
 			err = f2fs_do_write_data_page(&fio);
 			if (err) {
 				if (err == -ENOMEM) {
-					congestion_wait(BLK_RW_ASYNC,
-							DEFAULT_IO_TIMEOUT);
-					cond_resched();
+					memalloc_retry_wait(GFP_NOFS);
 					goto retry;
 				}
 				unlock_page(page);
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 040b6d02e1d8..be9006d6213f 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -10,7 +10,6 @@
 #include <linux/fs.h>
 #include <linux/statfs.h>
 #include <linux/buffer_head.h>
-#include <linux/backing-dev.h>
 #include <linux/kthread.h>
 #include <linux/parser.h>
 #include <linux/mount.h>
@@ -2415,8 +2414,7 @@ static ssize_t f2fs_quota_read(struct super_block *sb, int type, char *data,
 		page = read_cache_page_gfp(mapping, blkidx, GFP_NOFS);
 		if (IS_ERR(page)) {
 			if (PTR_ERR(page) == -ENOMEM) {
-				congestion_wait(BLK_RW_ASYNC,
-						DEFAULT_IO_TIMEOUT);
+				memalloc_retry_wait(GFP_NOFS);
 				goto repeat;
 			}
 			set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
index 6f49bf39183c..c557a030acfe 100644
--- a/fs/xfs/kmem.c
+++ b/fs/xfs/kmem.c
@@ -4,7 +4,6 @@
  * All Rights Reserved.
  */
 #include "xfs.h"
-#include <linux/backing-dev.h>
 #include "xfs_message.h"
 #include "xfs_trace.h"
 
@@ -26,6 +25,6 @@ kmem_alloc(size_t size, xfs_km_flags_t flags)
 	"%s(%u) possible memory allocation deadlock size %u in %s (mode:0x%x)",
 				current->comm, current->pid,
 				(unsigned int)size, __func__, lflags);
-		congestion_wait(BLK_RW_ASYNC, HZ/50);
+		memalloc_retry_wait(lflags);
 	} while (1);
 }
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 631c5a61d89b..6c45e3fa56f4 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -394,7 +394,7 @@ xfs_buf_alloc_pages(
 		}
 
 		XFS_STATS_INC(bp->b_mount, xb_page_retries);
-		congestion_wait(BLK_RW_ASYNC, HZ / 50);
+		memalloc_retry_wait(gfp_mask);
 	}
 	return 0;
 }
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index aca874d33fe6..f2f2a5b28808 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -214,6 +214,27 @@ static inline void fs_reclaim_acquire(gfp_t gfp_mask) { }
 static inline void fs_reclaim_release(gfp_t gfp_mask) { }
 #endif
 
+/* Any memory-allocation retry loop should use
+ * memalloc_retry_wait(), and pass the flags for the most
+ * constrained allocation attempt that might have failed.
+ * This provides useful documentation of where loops are,
+ * and a central place to fine tune the waiting as the MM
+ * implementation changes.
+ */
+static inline void memalloc_retry_wait(gfp_t gfp_flags)
+{
+	gfp_flags = current_gfp_context(gfp_flags);
+	if ((gfp_flags & __GFP_DIRECT_RECLAIM) &&
+	    !(gfp_flags & __GFP_NORETRY))
+		/* Probably waited already, no need for much more */
+		schedule_timeout_uninterruptible(1);
+	else
+		/* Probably didn't wait, and has now released a lock,
+		 * so now is a good time to wait
+		 */
+		schedule_timeout_uninterruptible(HZ/50);
+}
+
 /**
  * might_alloc - Mark possible allocation sites
  * @gfp_mask: gfp_t flags that would be used to allocate
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 1e99ba1b9d72..f9584e8e8324 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -688,7 +688,7 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
 			return -EINTR;
 		}
 		trace_svc_alloc_arg_err(pages);
-		schedule_timeout(msecs_to_jiffies(500));
+		memalloc_retry_wait(GFP_KERNEL);
 	}
 	rqstp->rq_page_end = &rqstp->rq_pages[pages];
 	rqstp->rq_pages[pages] = NULL; /* this might be seen in nfsd_splice_actor() */
-- 
2.33.1

Re: [PATCH] MM: introduce memalloc_retry_wait()

[Dave Chinner]

On Wed, Nov 17, 2021 at 03:28:10PM +1100, NeilBrown wrote:
> 
> Various places in the kernel - largely in filesystems - respond to a
> memory allocation failure by looping around and re-trying.
.....
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index aca874d33fe6..f2f2a5b28808 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -214,6 +214,27 @@ static inline void fs_reclaim_acquire(gfp_t gfp_mask) { }
>  static inline void fs_reclaim_release(gfp_t gfp_mask) { }
>  #endif
>  
> +/* Any memory-allocation retry loop should use
> + * memalloc_retry_wait(), and pass the flags for the most
> + * constrained allocation attempt that might have failed.
> + * This provides useful documentation of where loops are,
> + * and a central place to fine tune the waiting as the MM
> + * implementation changes.
> + */
> +static inline void memalloc_retry_wait(gfp_t gfp_flags)
> +{
> +	gfp_flags = current_gfp_context(gfp_flags);
> +	if ((gfp_flags & __GFP_DIRECT_RECLAIM) &&
> +	    !(gfp_flags & __GFP_NORETRY))
> +		/* Probably waited already, no need for much more */
> +		schedule_timeout_uninterruptible(1);
> +	else
> +		/* Probably didn't wait, and has now released a lock,
> +		 * so now is a good time to wait
> +		 */
> +		schedule_timeout_uninterruptible(HZ/50);
> +}

The existing congestion_wait() calls io_schedule_timeout() under
TASK_UNINTERRUPTIBLE conditions.

Does changing all these calls just to a plain
schedule_timeout_uninterruptible() make any difference to behaviour?
At least process accounting will appear different (uninterruptible
sleep instead of IO wait), and I suspect that the block plug
flushing in io_schedule() might be a good idea to retain for all the
filesystems that call this function from IO-related routines.

Cheers,

Dave.

-- 
Dave Chinner
david@fromorbit.com

[PATCH v2] MM: introduce memalloc_retry_wait()

[NeilBrown]

Various places in the kernel - largely in filesystems - respond to a
memory allocation failure by looping around and re-trying.
Some of these cannot conveniently use __GFP_NOFAIL, for reasons such as:
 - a GFP_ATOMIC allocation, which __GFP_NOFAIL doesn't work on
 - a need to check for the process being signalled between failures
 - the possibility that other recovery actions could be performed
 - the allocation is quite deep in support code, and passing down an
   extra flag to say if __GFP_NOFAIL is wanted would be clumsy.

Many of these currently use congestion_wait() which (in almost all
cases) simply waits the given timeout - congestion isn't tracked for
most devices.

It isn't clear what the best delay is for loops, but it is clear that
the various filesystems shouldn't be responsible for choosing a timeout.

This patch introduces memalloc_retry_wait() with takes on that
responsibility.  Code that wants to retry a memory allocation can call
this function passing the GFP flags that were used.  It will wait
however is appropriate.

For now, it only considers __GFP_NORETRY and whatever
gfpflags_allow_blocking() tests.  If blocking is allowed without
__GFP_NORETRY, then alloc_page either made some reclaim progress, or
waited for a while, before failing.  So there is no need for much
further waiting.  memalloc_retry_wait() will wait until the current
jiffie ends.  If this condition is not met, then alloc_page() won't have
waited much if at all.  In that case memalloc_retry_wait() waits about
200ms.  This is the delay that most current loops uses.

linux/sched/mm.h needs to be included in some files now,
but linux/backing-dev.h does not.

Signed-off-by: NeilBrown <neilb@suse.de>
---

Switched to io_schedule_timeout(), and added some missing #includes.

 fs/ext4/extents.c        |  8 +++-----
 fs/ext4/inline.c         |  5 ++---
 fs/ext4/page-io.c        |  9 +++++----
 fs/f2fs/data.c           |  4 ++--
 fs/f2fs/gc.c             |  5 ++---
 fs/f2fs/inode.c          |  4 ++--
 fs/f2fs/node.c           |  4 ++--
 fs/f2fs/recovery.c       |  6 +++---
 fs/f2fs/segment.c        |  9 +++------
 fs/f2fs/super.c          |  5 ++---
 fs/xfs/kmem.c            |  3 +--
 fs/xfs/xfs_buf.c         |  2 +-
 include/linux/sched/mm.h | 26 ++++++++++++++++++++++++++
 net/sunrpc/svc_xprt.c    |  3 ++-
 14 files changed, 56 insertions(+), 37 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 0ecf819bf189..5582fba36b44 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -27,8 +27,8 @@
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 #include <linux/fiemap.h>
-#include <linux/backing-dev.h>
 #include <linux/iomap.h>
+#include <linux/sched/mm.h>
 #include "ext4_jbd2.h"
 #include "ext4_extents.h"
 #include "xattr.h"
@@ -4407,8 +4407,7 @@ int ext4_ext_truncate(handle_t *handle, struct inode *inode)
 	err = ext4_es_remove_extent(inode, last_block,
 				    EXT_MAX_BLOCKS - last_block);
 	if (err == -ENOMEM) {
-		cond_resched();
-		congestion_wait(BLK_RW_ASYNC, HZ/50);
+		memalloc_retry_wait(GFP_ATOMIC);
 		goto retry;
 	}
 	if (err)
@@ -4416,8 +4415,7 @@ int ext4_ext_truncate(handle_t *handle, struct inode *inode)
 retry_remove_space:
 	err = ext4_ext_remove_space(inode, last_block, EXT_MAX_BLOCKS - 1);
 	if (err == -ENOMEM) {
-		cond_resched();
-		congestion_wait(BLK_RW_ASYNC, HZ/50);
+		memalloc_retry_wait(GFP_ATOMIC);
 		goto retry_remove_space;
 	}
 	return err;
diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 39a1ab129fdc..635bcf68a67e 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -7,7 +7,7 @@
 #include <linux/iomap.h>
 #include <linux/fiemap.h>
 #include <linux/iversion.h>
-#include <linux/backing-dev.h>
+#include <linux/sched/mm.h>
 
 #include "ext4_jbd2.h"
 #include "ext4.h"
@@ -1929,8 +1929,7 @@ int ext4_inline_data_truncate(struct inode *inode, int *has_inline)
 retry:
 			err = ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
 			if (err == -ENOMEM) {
-				cond_resched();
-				congestion_wait(BLK_RW_ASYNC, HZ/50);
+				memalloc_retry_wait(GFP_ATOMIC);
 				goto retry;
 			}
 			if (err)
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 9cb261714991..1d370364230e 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -24,7 +24,7 @@
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/mm.h>
-#include <linux/backing-dev.h>
+#include <linux/sched/mm.h>
 
 #include "ext4_jbd2.h"
 #include "xattr.h"
@@ -523,12 +523,13 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 			ret = PTR_ERR(bounce_page);
 			if (ret == -ENOMEM &&
 			    (io->io_bio || wbc->sync_mode == WB_SYNC_ALL)) {
-				gfp_flags = GFP_NOFS;
+				gfp_t new_gfp_flags = GFP_NOFS;
 				if (io->io_bio)
 					ext4_io_submit(io);
 				else
-					gfp_flags |= __GFP_NOFAIL;
-				congestion_wait(BLK_RW_ASYNC, HZ/50);
+					new_gfp_flags |= __GFP_NOFAIL;
+				memalloc_retry_wait(gfp_flags);
+				gfp_flags = new_gfp_flags;
 				goto retry_encrypt;
 			}
 
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 9f754aaef558..aacf5e4dcc57 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -8,9 +8,9 @@
 #include <linux/fs.h>
 #include <linux/f2fs_fs.h>
 #include <linux/buffer_head.h>
+#include <linux/sched/mm.h>
 #include <linux/mpage.h>
 #include <linux/writeback.h>
-#include <linux/backing-dev.h>
 #include <linux/pagevec.h>
 #include <linux/blkdev.h>
 #include <linux/bio.h>
@@ -2542,7 +2542,7 @@ int f2fs_encrypt_one_page(struct f2fs_io_info *fio)
 		/* flush pending IOs and wait for a while in the ENOMEM case */
 		if (PTR_ERR(fio->encrypted_page) == -ENOMEM) {
 			f2fs_flush_merged_writes(fio->sbi);
-			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+			memalloc_retry_wait(GFP_NOFS);
 			gfp_flags |= __GFP_NOFAIL;
 			goto retry_encrypt;
 		}
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index a946ce0ead34..374bbb5294d9 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -7,7 +7,6 @@
  */
 #include <linux/fs.h>
 #include <linux/module.h>
-#include <linux/backing-dev.h>
 #include <linux/init.h>
 #include <linux/f2fs_fs.h>
 #include <linux/kthread.h>
@@ -15,6 +14,7 @@
 #include <linux/freezer.h>
 #include <linux/sched/signal.h>
 #include <linux/random.h>
+#include <linux/sched/mm.h>
 
 #include "f2fs.h"
 #include "node.h"
@@ -1375,8 +1375,7 @@ static int move_data_page(struct inode *inode, block_t bidx, int gc_type,
 		if (err) {
 			clear_page_private_gcing(page);
 			if (err == -ENOMEM) {
-				congestion_wait(BLK_RW_ASYNC,
-						DEFAULT_IO_TIMEOUT);
+				memalloc_retry_wait(GFP_NOFS);
 				goto retry;
 			}
 			if (is_dirty)
diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 0f8b2df3e1e0..4c11254a07d4 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -8,8 +8,8 @@
 #include <linux/fs.h>
 #include <linux/f2fs_fs.h>
 #include <linux/buffer_head.h>
-#include <linux/backing-dev.h>
 #include <linux/writeback.h>
+#include <linux/sched/mm.h>
 
 #include "f2fs.h"
 #include "node.h"
@@ -562,7 +562,7 @@ struct inode *f2fs_iget_retry(struct super_block *sb, unsigned long ino)
 	inode = f2fs_iget(sb, ino);
 	if (IS_ERR(inode)) {
 		if (PTR_ERR(inode) == -ENOMEM) {
-			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+			memalloc_retry_wait(GFP_NOFS);
 			goto retry;
 		}
 	}
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 556fcd8457f3..219506ca9a97 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -8,7 +8,7 @@
 #include <linux/fs.h>
 #include <linux/f2fs_fs.h>
 #include <linux/mpage.h>
-#include <linux/backing-dev.h>
+#include <linux/sched/mm.h>
 #include <linux/blkdev.h>
 #include <linux/pagevec.h>
 #include <linux/swap.h>
@@ -2750,7 +2750,7 @@ int f2fs_recover_inode_page(struct f2fs_sb_info *sbi, struct page *page)
 retry:
 	ipage = f2fs_grab_cache_page(NODE_MAPPING(sbi), ino, false);
 	if (!ipage) {
-		congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+		memalloc_retry_wait(GFP_NOFS);
 		goto retry;
 	}
 
diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c
index 6a1b4668d933..d1664a0567ef 100644
--- a/fs/f2fs/recovery.c
+++ b/fs/f2fs/recovery.c
@@ -8,6 +8,7 @@
 #include <asm/unaligned.h>
 #include <linux/fs.h>
 #include <linux/f2fs_fs.h>
+#include <linux/sched/mm.h>
 #include "f2fs.h"
 #include "node.h"
 #include "segment.h"
@@ -587,7 +588,7 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,
 	err = f2fs_get_dnode_of_data(&dn, start, ALLOC_NODE);
 	if (err) {
 		if (err == -ENOMEM) {
-			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+			memalloc_retry_wait(GFP_NOFS);
 			goto retry_dn;
 		}
 		goto out;
@@ -670,8 +671,7 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,
 			err = check_index_in_prev_nodes(sbi, dest, &dn);
 			if (err) {
 				if (err == -ENOMEM) {
-					congestion_wait(BLK_RW_ASYNC,
-							DEFAULT_IO_TIMEOUT);
+					memalloc_retry_wait(GFP_NOFS);
 					goto retry_prev;
 				}
 				goto err;
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index df9ed75f0b7a..40fdb4a8daeb 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -9,6 +9,7 @@
 #include <linux/f2fs_fs.h>
 #include <linux/bio.h>
 #include <linux/blkdev.h>
+#include <linux/sched/mm.h>
 #include <linux/prefetch.h>
 #include <linux/kthread.h>
 #include <linux/swap.h>
@@ -245,9 +246,7 @@ static int __revoke_inmem_pages(struct inode *inode,
 								LOOKUP_NODE);
 			if (err) {
 				if (err == -ENOMEM) {
-					congestion_wait(BLK_RW_ASYNC,
-							DEFAULT_IO_TIMEOUT);
-					cond_resched();
+					memalloc_retry_wait(GFP_NOFS);
 					goto retry;
 				}
 				err = -EAGAIN;
@@ -424,9 +423,7 @@ static int __f2fs_commit_inmem_pages(struct inode *inode)
 			err = f2fs_do_write_data_page(&fio);
 			if (err) {
 				if (err == -ENOMEM) {
-					congestion_wait(BLK_RW_ASYNC,
-							DEFAULT_IO_TIMEOUT);
-					cond_resched();
+					memalloc_retry_wait(GFP_NOFS);
 					goto retry;
 				}
 				unlock_page(page);
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 040b6d02e1d8..3bace24f8800 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -8,9 +8,9 @@
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/fs.h>
+#include <linux/sched/mm.h>
 #include <linux/statfs.h>
 #include <linux/buffer_head.h>
-#include <linux/backing-dev.h>
 #include <linux/kthread.h>
 #include <linux/parser.h>
 #include <linux/mount.h>
@@ -2415,8 +2415,7 @@ static ssize_t f2fs_quota_read(struct super_block *sb, int type, char *data,
 		page = read_cache_page_gfp(mapping, blkidx, GFP_NOFS);
 		if (IS_ERR(page)) {
 			if (PTR_ERR(page) == -ENOMEM) {
-				congestion_wait(BLK_RW_ASYNC,
-						DEFAULT_IO_TIMEOUT);
+				memalloc_retry_wait(GFP_NOFS);
 				goto repeat;
 			}
 			set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
index 6f49bf39183c..c557a030acfe 100644
--- a/fs/xfs/kmem.c
+++ b/fs/xfs/kmem.c
@@ -4,7 +4,6 @@
  * All Rights Reserved.
  */
 #include "xfs.h"
-#include <linux/backing-dev.h>
 #include "xfs_message.h"
 #include "xfs_trace.h"
 
@@ -26,6 +25,6 @@ kmem_alloc(size_t size, xfs_km_flags_t flags)
 	"%s(%u) possible memory allocation deadlock size %u in %s (mode:0x%x)",
 				current->comm, current->pid,
 				(unsigned int)size, __func__, lflags);
-		congestion_wait(BLK_RW_ASYNC, HZ/50);
+		memalloc_retry_wait(lflags);
 	} while (1);
 }
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 631c5a61d89b..6c45e3fa56f4 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -394,7 +394,7 @@ xfs_buf_alloc_pages(
 		}
 
 		XFS_STATS_INC(bp->b_mount, xb_page_retries);
-		congestion_wait(BLK_RW_ASYNC, HZ / 50);
+		memalloc_retry_wait(gfp_mask);
 	}
 	return 0;
 }
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index aca874d33fe6..aa5f09ca5bcf 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -214,6 +214,32 @@ static inline void fs_reclaim_acquire(gfp_t gfp_mask) { }
 static inline void fs_reclaim_release(gfp_t gfp_mask) { }
 #endif
 
+/* Any memory-allocation retry loop should use
+ * memalloc_retry_wait(), and pass the flags for the most
+ * constrained allocation attempt that might have failed.
+ * This provides useful documentation of where loops are,
+ * and a central place to fine tune the waiting as the MM
+ * implementation changes.
+ */
+static inline void memalloc_retry_wait(gfp_t gfp_flags)
+{
+	/* We use io_schedule_timeout because waiting for memory
+	 * typically included waiting for dirty pages to be
+	 * written out, which requires IO.
+	 */
+	__set_current_state(TASK_UNINTERRUPTIBLE);
+	gfp_flags = current_gfp_context(gfp_flags);
+	if (gfpflags_allow_blocking(gfp_flags) &&
+	    !(gfp_flags & __GFP_NORETRY))
+		/* Probably waited already, no need for much more */
+		io_schedule_timeout(1);
+	else
+		/* Probably didn't wait, and has now released a lock,
+		 * so now is a good time to wait
+		 */
+		io_schedule_timeout(HZ/50);
+}
+
 /**
  * might_alloc - Mark possible allocation sites
  * @gfp_mask: gfp_t flags that would be used to allocate
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 1e99ba1b9d72..9cb18b822ab2 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -6,6 +6,7 @@
  */
 
 #include <linux/sched.h>
+#include <linux/sched/mm.h>
 #include <linux/errno.h>
 #include <linux/freezer.h>
 #include <linux/kthread.h>
@@ -688,7 +689,7 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
 			return -EINTR;
 		}
 		trace_svc_alloc_arg_err(pages);
-		schedule_timeout(msecs_to_jiffies(500));
+		memalloc_retry_wait(GFP_KERNEL);
 	}
 	rqstp->rq_page_end = &rqstp->rq_pages[pages];
 	rqstp->rq_pages[pages] = NULL; /* this might be seen in nfsd_splice_actor() */
-- 
2.33.1

Re: [PATCH v2] MM: introduce memalloc_retry_wait()

[Chuck Lever III]

> On Nov 21, 2021, at 8:15 PM, NeilBrown <neilb@suse.de> wrote:
> 
> 
> Various places in the kernel - largely in filesystems - respond to a
> memory allocation failure by looping around and re-trying.
> Some of these cannot conveniently use __GFP_NOFAIL, for reasons such as:
> - a GFP_ATOMIC allocation, which __GFP_NOFAIL doesn't work on
> - a need to check for the process being signalled between failures
> - the possibility that other recovery actions could be performed
> - the allocation is quite deep in support code, and passing down an
>   extra flag to say if __GFP_NOFAIL is wanted would be clumsy.
> 
> Many of these currently use congestion_wait() which (in almost all
> cases) simply waits the given timeout - congestion isn't tracked for
> most devices.
> 
> It isn't clear what the best delay is for loops, but it is clear that
> the various filesystems shouldn't be responsible for choosing a timeout.
> 
> This patch introduces memalloc_retry_wait() with takes on that
> responsibility.  Code that wants to retry a memory allocation can call
> this function passing the GFP flags that were used.  It will wait
> however is appropriate.
> 
> For now, it only considers __GFP_NORETRY and whatever
> gfpflags_allow_blocking() tests.  If blocking is allowed without
> __GFP_NORETRY, then alloc_page either made some reclaim progress, or
> waited for a while, before failing.  So there is no need for much
> further waiting.  memalloc_retry_wait() will wait until the current
> jiffie ends.  If this condition is not met, then alloc_page() won't have
> waited much if at all.  In that case memalloc_retry_wait() waits about
> 200ms.  This is the delay that most current loops uses.
> 
> linux/sched/mm.h needs to be included in some files now,
> but linux/backing-dev.h does not.
> 
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
> 
> Switched to io_schedule_timeout(), and added some missing #includes.
> 
> fs/ext4/extents.c        |  8 +++-----
> fs/ext4/inline.c         |  5 ++---
> fs/ext4/page-io.c        |  9 +++++----
> fs/f2fs/data.c           |  4 ++--
> fs/f2fs/gc.c             |  5 ++---
> fs/f2fs/inode.c          |  4 ++--
> fs/f2fs/node.c           |  4 ++--
> fs/f2fs/recovery.c       |  6 +++---
> fs/f2fs/segment.c        |  9 +++------
> fs/f2fs/super.c          |  5 ++---
> fs/xfs/kmem.c            |  3 +--
> fs/xfs/xfs_buf.c         |  2 +-
> include/linux/sched/mm.h | 26 ++++++++++++++++++++++++++
> net/sunrpc/svc_xprt.c    |  3 ++-
> 14 files changed, 56 insertions(+), 37 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 0ecf819bf189..5582fba36b44 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -27,8 +27,8 @@
> #include <linux/slab.h>
> #include <linux/uaccess.h>
> #include <linux/fiemap.h>
> -#include <linux/backing-dev.h>
> #include <linux/iomap.h>
> +#include <linux/sched/mm.h>
> #include "ext4_jbd2.h"
> #include "ext4_extents.h"
> #include "xattr.h"
> @@ -4407,8 +4407,7 @@ int ext4_ext_truncate(handle_t *handle, struct inode *inode)
> 	err = ext4_es_remove_extent(inode, last_block,
> 				    EXT_MAX_BLOCKS - last_block);
> 	if (err == -ENOMEM) {
> -		cond_resched();
> -		congestion_wait(BLK_RW_ASYNC, HZ/50);
> +		memalloc_retry_wait(GFP_ATOMIC);
> 		goto retry;
> 	}
> 	if (err)
> @@ -4416,8 +4415,7 @@ int ext4_ext_truncate(handle_t *handle, struct inode *inode)
> retry_remove_space:
> 	err = ext4_ext_remove_space(inode, last_block, EXT_MAX_BLOCKS - 1);
> 	if (err == -ENOMEM) {
> -		cond_resched();
> -		congestion_wait(BLK_RW_ASYNC, HZ/50);
> +		memalloc_retry_wait(GFP_ATOMIC);
> 		goto retry_remove_space;
> 	}
> 	return err;
> diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
> index 39a1ab129fdc..635bcf68a67e 100644
> --- a/fs/ext4/inline.c
> +++ b/fs/ext4/inline.c
> @@ -7,7 +7,7 @@
> #include <linux/iomap.h>
> #include <linux/fiemap.h>
> #include <linux/iversion.h>
> -#include <linux/backing-dev.h>
> +#include <linux/sched/mm.h>
> 
> #include "ext4_jbd2.h"
> #include "ext4.h"
> @@ -1929,8 +1929,7 @@ int ext4_inline_data_truncate(struct inode *inode, int *has_inline)
> retry:
> 			err = ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
> 			if (err == -ENOMEM) {
> -				cond_resched();
> -				congestion_wait(BLK_RW_ASYNC, HZ/50);
> +				memalloc_retry_wait(GFP_ATOMIC);
> 				goto retry;
> 			}
> 			if (err)
> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
> index 9cb261714991..1d370364230e 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -24,7 +24,7 @@
> #include <linux/kernel.h>
> #include <linux/slab.h>
> #include <linux/mm.h>
> -#include <linux/backing-dev.h>
> +#include <linux/sched/mm.h>
> 
> #include "ext4_jbd2.h"
> #include "xattr.h"
> @@ -523,12 +523,13 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
> 			ret = PTR_ERR(bounce_page);
> 			if (ret == -ENOMEM &&
> 			    (io->io_bio || wbc->sync_mode == WB_SYNC_ALL)) {
> -				gfp_flags = GFP_NOFS;
> +				gfp_t new_gfp_flags = GFP_NOFS;
> 				if (io->io_bio)
> 					ext4_io_submit(io);
> 				else
> -					gfp_flags |= __GFP_NOFAIL;
> -				congestion_wait(BLK_RW_ASYNC, HZ/50);
> +					new_gfp_flags |= __GFP_NOFAIL;
> +				memalloc_retry_wait(gfp_flags);
> +				gfp_flags = new_gfp_flags;
> 				goto retry_encrypt;
> 			}
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 9f754aaef558..aacf5e4dcc57 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -8,9 +8,9 @@
> #include <linux/fs.h>
> #include <linux/f2fs_fs.h>
> #include <linux/buffer_head.h>
> +#include <linux/sched/mm.h>
> #include <linux/mpage.h>
> #include <linux/writeback.h>
> -#include <linux/backing-dev.h>
> #include <linux/pagevec.h>
> #include <linux/blkdev.h>
> #include <linux/bio.h>
> @@ -2542,7 +2542,7 @@ int f2fs_encrypt_one_page(struct f2fs_io_info *fio)
> 		/* flush pending IOs and wait for a while in the ENOMEM case */
> 		if (PTR_ERR(fio->encrypted_page) == -ENOMEM) {
> 			f2fs_flush_merged_writes(fio->sbi);
> -			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
> +			memalloc_retry_wait(GFP_NOFS);
> 			gfp_flags |= __GFP_NOFAIL;
> 			goto retry_encrypt;
> 		}
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index a946ce0ead34..374bbb5294d9 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -7,7 +7,6 @@
>  */
> #include <linux/fs.h>
> #include <linux/module.h>
> -#include <linux/backing-dev.h>
> #include <linux/init.h>
> #include <linux/f2fs_fs.h>
> #include <linux/kthread.h>
> @@ -15,6 +14,7 @@
> #include <linux/freezer.h>
> #include <linux/sched/signal.h>
> #include <linux/random.h>
> +#include <linux/sched/mm.h>
> 
> #include "f2fs.h"
> #include "node.h"
> @@ -1375,8 +1375,7 @@ static int move_data_page(struct inode *inode, block_t bidx, int gc_type,
> 		if (err) {
> 			clear_page_private_gcing(page);
> 			if (err == -ENOMEM) {
> -				congestion_wait(BLK_RW_ASYNC,
> -						DEFAULT_IO_TIMEOUT);
> +				memalloc_retry_wait(GFP_NOFS);
> 				goto retry;
> 			}
> 			if (is_dirty)
> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> index 0f8b2df3e1e0..4c11254a07d4 100644
> --- a/fs/f2fs/inode.c
> +++ b/fs/f2fs/inode.c
> @@ -8,8 +8,8 @@
> #include <linux/fs.h>
> #include <linux/f2fs_fs.h>
> #include <linux/buffer_head.h>
> -#include <linux/backing-dev.h>
> #include <linux/writeback.h>
> +#include <linux/sched/mm.h>
> 
> #include "f2fs.h"
> #include "node.h"
> @@ -562,7 +562,7 @@ struct inode *f2fs_iget_retry(struct super_block *sb, unsigned long ino)
> 	inode = f2fs_iget(sb, ino);
> 	if (IS_ERR(inode)) {
> 		if (PTR_ERR(inode) == -ENOMEM) {
> -			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
> +			memalloc_retry_wait(GFP_NOFS);
> 			goto retry;
> 		}
> 	}
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 556fcd8457f3..219506ca9a97 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -8,7 +8,7 @@
> #include <linux/fs.h>
> #include <linux/f2fs_fs.h>
> #include <linux/mpage.h>
> -#include <linux/backing-dev.h>
> +#include <linux/sched/mm.h>
> #include <linux/blkdev.h>
> #include <linux/pagevec.h>
> #include <linux/swap.h>
> @@ -2750,7 +2750,7 @@ int f2fs_recover_inode_page(struct f2fs_sb_info *sbi, struct page *page)
> retry:
> 	ipage = f2fs_grab_cache_page(NODE_MAPPING(sbi), ino, false);
> 	if (!ipage) {
> -		congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
> +		memalloc_retry_wait(GFP_NOFS);
> 		goto retry;
> 	}
> 
> diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c
> index 6a1b4668d933..d1664a0567ef 100644
> --- a/fs/f2fs/recovery.c
> +++ b/fs/f2fs/recovery.c
> @@ -8,6 +8,7 @@
> #include <asm/unaligned.h>
> #include <linux/fs.h>
> #include <linux/f2fs_fs.h>
> +#include <linux/sched/mm.h>
> #include "f2fs.h"
> #include "node.h"
> #include "segment.h"
> @@ -587,7 +588,7 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,
> 	err = f2fs_get_dnode_of_data(&dn, start, ALLOC_NODE);
> 	if (err) {
> 		if (err == -ENOMEM) {
> -			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
> +			memalloc_retry_wait(GFP_NOFS);
> 			goto retry_dn;
> 		}
> 		goto out;
> @@ -670,8 +671,7 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,
> 			err = check_index_in_prev_nodes(sbi, dest, &dn);
> 			if (err) {
> 				if (err == -ENOMEM) {
> -					congestion_wait(BLK_RW_ASYNC,
> -							DEFAULT_IO_TIMEOUT);
> +					memalloc_retry_wait(GFP_NOFS);
> 					goto retry_prev;
> 				}
> 				goto err;
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index df9ed75f0b7a..40fdb4a8daeb 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -9,6 +9,7 @@
> #include <linux/f2fs_fs.h>
> #include <linux/bio.h>
> #include <linux/blkdev.h>
> +#include <linux/sched/mm.h>
> #include <linux/prefetch.h>
> #include <linux/kthread.h>
> #include <linux/swap.h>
> @@ -245,9 +246,7 @@ static int __revoke_inmem_pages(struct inode *inode,
> 								LOOKUP_NODE);
> 			if (err) {
> 				if (err == -ENOMEM) {
> -					congestion_wait(BLK_RW_ASYNC,
> -							DEFAULT_IO_TIMEOUT);
> -					cond_resched();
> +					memalloc_retry_wait(GFP_NOFS);
> 					goto retry;
> 				}
> 				err = -EAGAIN;
> @@ -424,9 +423,7 @@ static int __f2fs_commit_inmem_pages(struct inode *inode)
> 			err = f2fs_do_write_data_page(&fio);
> 			if (err) {
> 				if (err == -ENOMEM) {
> -					congestion_wait(BLK_RW_ASYNC,
> -							DEFAULT_IO_TIMEOUT);
> -					cond_resched();
> +					memalloc_retry_wait(GFP_NOFS);
> 					goto retry;
> 				}
> 				unlock_page(page);
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 040b6d02e1d8..3bace24f8800 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -8,9 +8,9 @@
> #include <linux/module.h>
> #include <linux/init.h>
> #include <linux/fs.h>
> +#include <linux/sched/mm.h>
> #include <linux/statfs.h>
> #include <linux/buffer_head.h>
> -#include <linux/backing-dev.h>
> #include <linux/kthread.h>
> #include <linux/parser.h>
> #include <linux/mount.h>
> @@ -2415,8 +2415,7 @@ static ssize_t f2fs_quota_read(struct super_block *sb, int type, char *data,
> 		page = read_cache_page_gfp(mapping, blkidx, GFP_NOFS);
> 		if (IS_ERR(page)) {
> 			if (PTR_ERR(page) == -ENOMEM) {
> -				congestion_wait(BLK_RW_ASYNC,
> -						DEFAULT_IO_TIMEOUT);
> +				memalloc_retry_wait(GFP_NOFS);
> 				goto repeat;
> 			}
> 			set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
> diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> index 6f49bf39183c..c557a030acfe 100644
> --- a/fs/xfs/kmem.c
> +++ b/fs/xfs/kmem.c
> @@ -4,7 +4,6 @@
>  * All Rights Reserved.
>  */
> #include "xfs.h"
> -#include <linux/backing-dev.h>
> #include "xfs_message.h"
> #include "xfs_trace.h"
> 
> @@ -26,6 +25,6 @@ kmem_alloc(size_t size, xfs_km_flags_t flags)
> 	"%s(%u) possible memory allocation deadlock size %u in %s (mode:0x%x)",
> 				current->comm, current->pid,
> 				(unsigned int)size, __func__, lflags);
> -		congestion_wait(BLK_RW_ASYNC, HZ/50);
> +		memalloc_retry_wait(lflags);
> 	} while (1);
> }
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 631c5a61d89b..6c45e3fa56f4 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -394,7 +394,7 @@ xfs_buf_alloc_pages(
> 		}
> 
> 		XFS_STATS_INC(bp->b_mount, xb_page_retries);
> -		congestion_wait(BLK_RW_ASYNC, HZ / 50);
> +		memalloc_retry_wait(gfp_mask);
> 	}
> 	return 0;
> }
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index aca874d33fe6..aa5f09ca5bcf 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -214,6 +214,32 @@ static inline void fs_reclaim_acquire(gfp_t gfp_mask) { }
> static inline void fs_reclaim_release(gfp_t gfp_mask) { }
> #endif
> 
> +/* Any memory-allocation retry loop should use
> + * memalloc_retry_wait(), and pass the flags for the most
> + * constrained allocation attempt that might have failed.
> + * This provides useful documentation of where loops are,

"useful documentation" is a good thing, but to me that means
there's some auditing mechanism like a trace point. Getting
to this function seems like an exceptional event that should
be noted externally.

If memalloc_retry_wait() had a trace point, I'd be inclined
to remove trace_svc_alloc_arg_err().

(This comment is not an objection to your patch).


> + * and a central place to fine tune the waiting as the MM
> + * implementation changes.
> + */
> +static inline void memalloc_retry_wait(gfp_t gfp_flags)
> +{
> +	/* We use io_schedule_timeout because waiting for memory
> +	 * typically included waiting for dirty pages to be
> +	 * written out, which requires IO.
> +	 */
> +	__set_current_state(TASK_UNINTERRUPTIBLE);
> +	gfp_flags = current_gfp_context(gfp_flags);
> +	if (gfpflags_allow_blocking(gfp_flags) &&
> +	    !(gfp_flags & __GFP_NORETRY))
> +		/* Probably waited already, no need for much more */
> +		io_schedule_timeout(1);
> +	else
> +		/* Probably didn't wait, and has now released a lock,
> +		 * so now is a good time to wait
> +		 */
> +		io_schedule_timeout(HZ/50);
> +}
> +
> /**
>  * might_alloc - Mark possible allocation sites
>  * @gfp_mask: gfp_t flags that would be used to allocate
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index 1e99ba1b9d72..9cb18b822ab2 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -6,6 +6,7 @@
>  */
> 
> #include <linux/sched.h>
> +#include <linux/sched/mm.h>
> #include <linux/errno.h>
> #include <linux/freezer.h>
> #include <linux/kthread.h>
> @@ -688,7 +689,7 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
> 			return -EINTR;
> 		}
> 		trace_svc_alloc_arg_err(pages);
> -		schedule_timeout(msecs_to_jiffies(500));
> +		memalloc_retry_wait(GFP_KERNEL);
> 	}
> 	rqstp->rq_page_end = &rqstp->rq_pages[pages];
> 	rqstp->rq_pages[pages] = NULL; /* this might be seen in nfsd_splice_actor() */
> -- 
> 2.33.1
> 

--
Chuck Lever

Re: [PATCH] MM: introduce memalloc_retry_wait()

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 3747 bytes --]

Hi NeilBrown,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on jaegeuk-f2fs/dev-test]
[also build test ERROR on v5.16-rc1 next-20211118]
[cannot apply to tytso-ext4/dev xfs-linux/for-next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/NeilBrown/MM-introduce-memalloc_retry_wait/20211117-122932
base:   https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git dev-test
config: riscv-randconfig-r004-20211118 (attached as .config)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install riscv cross compiling tool for clang build
        # apt-get install binutils-riscv64-linux-gnu
        # https://github.com/0day-ci/linux/commit/1da355dc212c5f6ade3a21d4a5b1cfaf6b48ff0f
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review NeilBrown/MM-introduce-memalloc_retry_wait/20211117-122932
        git checkout 1da355dc212c5f6ade3a21d4a5b1cfaf6b48ff0f
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=riscv 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> fs/f2fs/super.c:2417:5: error: implicit declaration of function 'memalloc_retry_wait' [-Werror,-Wimplicit-function-declaration]
                                   memalloc_retry_wait(GFP_NOFS);
                                   ^
   1 error generated.


vim +/memalloc_retry_wait +2417 fs/f2fs/super.c

  2389	
  2390	#ifdef CONFIG_QUOTA
  2391	/* Read data from quotafile */
  2392	static ssize_t f2fs_quota_read(struct super_block *sb, int type, char *data,
  2393				       size_t len, loff_t off)
  2394	{
  2395		struct inode *inode = sb_dqopt(sb)->files[type];
  2396		struct address_space *mapping = inode->i_mapping;
  2397		block_t blkidx = F2FS_BYTES_TO_BLK(off);
  2398		int offset = off & (sb->s_blocksize - 1);
  2399		int tocopy;
  2400		size_t toread;
  2401		loff_t i_size = i_size_read(inode);
  2402		struct page *page;
  2403		char *kaddr;
  2404	
  2405		if (off > i_size)
  2406			return 0;
  2407	
  2408		if (off + len > i_size)
  2409			len = i_size - off;
  2410		toread = len;
  2411		while (toread > 0) {
  2412			tocopy = min_t(unsigned long, sb->s_blocksize - offset, toread);
  2413	repeat:
  2414			page = read_cache_page_gfp(mapping, blkidx, GFP_NOFS);
  2415			if (IS_ERR(page)) {
  2416				if (PTR_ERR(page) == -ENOMEM) {
> 2417					memalloc_retry_wait(GFP_NOFS);
  2418					goto repeat;
  2419				}
  2420				set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
  2421				return PTR_ERR(page);
  2422			}
  2423	
  2424			lock_page(page);
  2425	
  2426			if (unlikely(page->mapping != mapping)) {
  2427				f2fs_put_page(page, 1);
  2428				goto repeat;
  2429			}
  2430			if (unlikely(!PageUptodate(page))) {
  2431				f2fs_put_page(page, 1);
  2432				set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
  2433				return -EIO;
  2434			}
  2435	
  2436			kaddr = kmap_atomic(page);
  2437			memcpy(data, kaddr + offset, tocopy);
  2438			kunmap_atomic(kaddr);
  2439			f2fs_put_page(page, 1);
  2440	
  2441			offset = 0;
  2442			toread -= tocopy;
  2443			data += tocopy;
  2444			blkidx++;
  2445		}
  2446		return len;
  2447	}
  2448	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 34391 bytes --]

Re: [PATCH] MM: introduce memalloc_retry_wait()

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 3760 bytes --]

Hi NeilBrown,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on jaegeuk-f2fs/dev-test]
[also build test ERROR on v5.16-rc1 next-20211118]
[cannot apply to xfs-linux/for-next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/NeilBrown/MM-introduce-memalloc_retry_wait/20211117-122932
base:   https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git dev-test
config: arc-randconfig-r043-20211117 (attached as .config)
compiler: arceb-elf-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/1da355dc212c5f6ade3a21d4a5b1cfaf6b48ff0f
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review NeilBrown/MM-introduce-memalloc_retry_wait/20211117-122932
        git checkout 1da355dc212c5f6ade3a21d4a5b1cfaf6b48ff0f
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross ARCH=arc 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   fs/f2fs/super.c: In function 'f2fs_quota_read':
>> fs/f2fs/super.c:2417:33: error: implicit declaration of function 'memalloc_retry_wait' [-Werror=implicit-function-declaration]
    2417 |                                 memalloc_retry_wait(GFP_NOFS);
         |                                 ^~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors


vim +/memalloc_retry_wait +2417 fs/f2fs/super.c

  2389	
  2390	#ifdef CONFIG_QUOTA
  2391	/* Read data from quotafile */
  2392	static ssize_t f2fs_quota_read(struct super_block *sb, int type, char *data,
  2393				       size_t len, loff_t off)
  2394	{
  2395		struct inode *inode = sb_dqopt(sb)->files[type];
  2396		struct address_space *mapping = inode->i_mapping;
  2397		block_t blkidx = F2FS_BYTES_TO_BLK(off);
  2398		int offset = off & (sb->s_blocksize - 1);
  2399		int tocopy;
  2400		size_t toread;
  2401		loff_t i_size = i_size_read(inode);
  2402		struct page *page;
  2403		char *kaddr;
  2404	
  2405		if (off > i_size)
  2406			return 0;
  2407	
  2408		if (off + len > i_size)
  2409			len = i_size - off;
  2410		toread = len;
  2411		while (toread > 0) {
  2412			tocopy = min_t(unsigned long, sb->s_blocksize - offset, toread);
  2413	repeat:
  2414			page = read_cache_page_gfp(mapping, blkidx, GFP_NOFS);
  2415			if (IS_ERR(page)) {
  2416				if (PTR_ERR(page) == -ENOMEM) {
> 2417					memalloc_retry_wait(GFP_NOFS);
  2418					goto repeat;
  2419				}
  2420				set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
  2421				return PTR_ERR(page);
  2422			}
  2423	
  2424			lock_page(page);
  2425	
  2426			if (unlikely(page->mapping != mapping)) {
  2427				f2fs_put_page(page, 1);
  2428				goto repeat;
  2429			}
  2430			if (unlikely(!PageUptodate(page))) {
  2431				f2fs_put_page(page, 1);
  2432				set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
  2433				return -EIO;
  2434			}
  2435	
  2436			kaddr = kmap_atomic(page);
  2437			memcpy(data, kaddr + offset, tocopy);
  2438			kunmap_atomic(kaddr);
  2439			f2fs_put_page(page, 1);
  2440	
  2441			offset = 0;
  2442			toread -= tocopy;
  2443			data += tocopy;
  2444			blkidx++;
  2445		}
  2446		return len;
  2447	}
  2448	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 31531 bytes --]