* [PATCH v4 1/3] filemap: Add a helper for filesystems implementing dropbehind
2025-08-19 14:18 [PATCH v4 0/3] Initial NFS client support for RWF_DONTCACHE Trond Myklebust
@ 2025-08-19 14:18 ` Trond Myklebust
2025-08-19 14:25 ` Christoph Hellwig
2025-08-19 14:18 ` [PATCH v4 2/3] filemap: Add a version of folio_end_writeback that ignores dropbehind Trond Myklebust
2025-08-19 14:18 ` [PATCH v4 3/3] NFS: Enable use of the RWF_DONTCACHE flag on the NFS client Trond Myklebust
2 siblings, 1 reply; 5+ messages in thread
From: Trond Myklebust @ 2025-08-19 14:18 UTC (permalink / raw)
To: Anna Schumaker; +Cc: linux-nfs, linux-fsdevel, Mike Snitzer, Matthew Wilcox
From: Trond Myklebust <trond.myklebust@hammerspace.com>
Add a helper to allow filesystems to attempt to free the 'dropbehind'
folio.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Link: https://lore.kernel.org/all/5588a06f6d5a2cf6746828e2d36e7ada668b1739.1745381692.git.trond.myklebust@hammerspace.com/
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
---
include/linux/pagemap.h | 1 +
mm/filemap.c | 5 +++--
2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 12a12dae727d..201b7c6f6441 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1221,6 +1221,7 @@ void folio_wait_writeback(struct folio *folio);
int folio_wait_writeback_killable(struct folio *folio);
void end_page_writeback(struct page *page);
void folio_end_writeback(struct folio *folio);
+void folio_end_dropbehind(struct folio *folio);
void folio_wait_stable(struct folio *folio);
void __folio_mark_dirty(struct folio *folio, struct address_space *, int warn);
void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb);
diff --git a/mm/filemap.c b/mm/filemap.c
index 751838ef05e5..71209ebbcc36 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1608,7 +1608,7 @@ static void filemap_end_dropbehind(struct folio *folio)
* completes. Do that now. If we fail, it's likely because of a big folio -
* just reset dropbehind for that case and latter completions should invalidate.
*/
-static void filemap_end_dropbehind_write(struct folio *folio)
+void folio_end_dropbehind(struct folio *folio)
{
if (!folio_test_dropbehind(folio))
return;
@@ -1625,6 +1625,7 @@ static void filemap_end_dropbehind_write(struct folio *folio)
folio_unlock(folio);
}
}
+EXPORT_SYMBOL(folio_end_dropbehind);
/**
* folio_end_writeback - End writeback against a folio.
@@ -1660,7 +1661,7 @@ void folio_end_writeback(struct folio *folio)
if (__folio_end_writeback(folio))
folio_wake_bit(folio, PG_writeback);
- filemap_end_dropbehind_write(folio);
+ folio_end_dropbehind(folio);
acct_reclaim_writeback(folio);
folio_put(folio);
}
--
2.50.1
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH v4 2/3] filemap: Add a version of folio_end_writeback that ignores dropbehind
2025-08-19 14:18 [PATCH v4 0/3] Initial NFS client support for RWF_DONTCACHE Trond Myklebust
2025-08-19 14:18 ` [PATCH v4 1/3] filemap: Add a helper for filesystems implementing dropbehind Trond Myklebust
@ 2025-08-19 14:18 ` Trond Myklebust
2025-08-19 14:18 ` [PATCH v4 3/3] NFS: Enable use of the RWF_DONTCACHE flag on the NFS client Trond Myklebust
2 siblings, 0 replies; 5+ messages in thread
From: Trond Myklebust @ 2025-08-19 14:18 UTC (permalink / raw)
To: Anna Schumaker; +Cc: linux-nfs, linux-fsdevel, Mike Snitzer, Matthew Wilcox
From: Trond Myklebust <trond.myklebust@hammerspace.com>
Filesystems such as NFS may need to defer dropbehind until after their
2-stage writes are done. This adds a helper
folio_end_writeback_no_dropbehind() that allows them to release the
writeback flag without immediately dropping the folio.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
include/linux/pagemap.h | 1 +
mm/filemap.c | 29 +++++++++++++++++++++++------
2 files changed, 24 insertions(+), 6 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 201b7c6f6441..5b26465358ce 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1221,6 +1221,7 @@ void folio_wait_writeback(struct folio *folio);
int folio_wait_writeback_killable(struct folio *folio);
void end_page_writeback(struct page *page);
void folio_end_writeback(struct folio *folio);
+void folio_end_writeback_no_dropbehind(struct folio *folio);
void folio_end_dropbehind(struct folio *folio);
void folio_wait_stable(struct folio *folio);
void __folio_mark_dirty(struct folio *folio, struct address_space *, int warn);
diff --git a/mm/filemap.c b/mm/filemap.c
index 71209ebbcc36..0cf147ca7c16 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1628,14 +1628,15 @@ void folio_end_dropbehind(struct folio *folio)
EXPORT_SYMBOL(folio_end_dropbehind);
/**
- * folio_end_writeback - End writeback against a folio.
+ * folio_end_writeback_no_dropbehind - End writeback against a folio.
* @folio: The folio.
*
* The folio must actually be under writeback.
+ * This call is intended for filesystems that need to defer dropbehind.
*
* Context: May be called from process or interrupt context.
*/
-void folio_end_writeback(struct folio *folio)
+void folio_end_writeback_no_dropbehind(struct folio *folio)
{
VM_BUG_ON_FOLIO(!folio_test_writeback(folio), folio);
@@ -1651,6 +1652,25 @@ void folio_end_writeback(struct folio *folio)
folio_rotate_reclaimable(folio);
}
+ if (__folio_end_writeback(folio))
+ folio_wake_bit(folio, PG_writeback);
+
+ acct_reclaim_writeback(folio);
+}
+EXPORT_SYMBOL(folio_end_writeback_no_dropbehind);
+
+/**
+ * folio_end_writeback - End writeback against a folio.
+ * @folio: The folio.
+ *
+ * The folio must actually be under writeback.
+ *
+ * Context: May be called from process or interrupt context.
+ */
+void folio_end_writeback(struct folio *folio)
+{
+ VM_BUG_ON_FOLIO(!folio_test_writeback(folio), folio);
+
/*
* Writeback does not hold a folio reference of its own, relying
* on truncation to wait for the clearing of PG_writeback.
@@ -1658,11 +1678,8 @@ void folio_end_writeback(struct folio *folio)
* reused before the folio_wake_bit().
*/
folio_get(folio);
- if (__folio_end_writeback(folio))
- folio_wake_bit(folio, PG_writeback);
-
+ folio_end_writeback_no_dropbehind(folio);
folio_end_dropbehind(folio);
- acct_reclaim_writeback(folio);
folio_put(folio);
}
EXPORT_SYMBOL(folio_end_writeback);
--
2.50.1
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH v4 3/3] NFS: Enable use of the RWF_DONTCACHE flag on the NFS client
2025-08-19 14:18 [PATCH v4 0/3] Initial NFS client support for RWF_DONTCACHE Trond Myklebust
2025-08-19 14:18 ` [PATCH v4 1/3] filemap: Add a helper for filesystems implementing dropbehind Trond Myklebust
2025-08-19 14:18 ` [PATCH v4 2/3] filemap: Add a version of folio_end_writeback that ignores dropbehind Trond Myklebust
@ 2025-08-19 14:18 ` Trond Myklebust
2 siblings, 0 replies; 5+ messages in thread
From: Trond Myklebust @ 2025-08-19 14:18 UTC (permalink / raw)
To: Anna Schumaker; +Cc: linux-nfs, linux-fsdevel, Mike Snitzer, Matthew Wilcox
From: Trond Myklebust <trond.myklebust@hammerspace.com>
The NFS client needs to defer dropbehind until after any writes to the
folio have been persisted on the server. Since this may be a 2 step
process, use folio_end_writeback_no_dropbehind() to allow release of the
writeback flag, and then call folio_end_dropbehind() once the COMMIT is
done.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
fs/nfs/file.c | 9 +++++----
fs/nfs/nfs4file.c | 1 +
fs/nfs/write.c | 4 +++-
3 files changed, 9 insertions(+), 5 deletions(-)
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 86e36c630f09..90610629862a 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -329,6 +329,8 @@ static bool nfs_want_read_modify_write(struct file *file, struct folio *folio,
if (pnfs_ld_read_whole_page(file_inode(file)))
return true;
+ if (folio_test_dropbehind(folio))
+ return false;
/* Open for reading too? */
if (file->f_mode & FMODE_READ)
return true;
@@ -348,7 +350,6 @@ static int nfs_write_begin(const struct kiocb *iocb,
loff_t pos, unsigned len, struct folio **foliop,
void **fsdata)
{
- fgf_t fgp = FGP_WRITEBEGIN;
struct folio *folio;
struct file *file = iocb->ki_filp;
int once_thru = 0;
@@ -357,10 +358,8 @@ static int nfs_write_begin(const struct kiocb *iocb,
dfprintk(PAGECACHE, "NFS: write_begin(%pD2(%lu), %u@%lld)\n",
file, mapping->host->i_ino, len, (long long) pos);
- fgp |= fgf_set_order(len);
start:
- folio = __filemap_get_folio(mapping, pos >> PAGE_SHIFT, fgp,
- mapping_gfp_mask(mapping));
+ folio = write_begin_get_folio(iocb, mapping, pos >> PAGE_SHIFT, len);
if (IS_ERR(folio))
return PTR_ERR(folio);
*foliop = folio;
@@ -372,6 +371,7 @@ static int nfs_write_begin(const struct kiocb *iocb,
} else if (!once_thru &&
nfs_want_read_modify_write(file, folio, pos, len)) {
once_thru = 1;
+ folio_clear_dropbehind(folio);
ret = nfs_read_folio(file, folio);
folio_put(folio);
if (!ret)
@@ -915,5 +915,6 @@ const struct file_operations nfs_file_operations = {
.splice_write = iter_file_splice_write,
.check_flags = nfs_check_flags,
.setlease = simple_nosetlease,
+ .fop_flags = FOP_DONTCACHE,
};
EXPORT_SYMBOL_GPL(nfs_file_operations);
diff --git a/fs/nfs/nfs4file.c b/fs/nfs/nfs4file.c
index 1d6b5f4230c9..654fda6f362c 100644
--- a/fs/nfs/nfs4file.c
+++ b/fs/nfs/nfs4file.c
@@ -454,4 +454,5 @@ const struct file_operations nfs4_file_operations = {
#else
.llseek = nfs_file_llseek,
#endif
+ .fop_flags = FOP_DONTCACHE,
};
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 8b7c04737967..079fc1af928f 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -338,7 +338,7 @@ static void nfs_folio_end_writeback(struct folio *folio)
{
struct nfs_server *nfss = NFS_SERVER(folio->mapping->host);
- folio_end_writeback(folio);
+ folio_end_writeback_no_dropbehind(folio);
if (atomic_long_dec_return(&nfss->writeback) <
NFS_CONGESTION_OFF_THRESH) {
nfss->write_congested = 0;
@@ -787,6 +787,8 @@ static void nfs_inode_remove_request(struct nfs_page *req)
clear_bit(PG_MAPPED, &req->wb_head->wb_flags);
}
spin_unlock(&mapping->i_private_lock);
+
+ folio_end_dropbehind(folio);
}
nfs_page_group_unlock(req);
--
2.50.1
^ permalink raw reply related [flat|nested] 5+ messages in thread