Re: [PATCH 0/2] Make task doing heavy writing killable

[Wu Fengguang <fengguang.wu@intel.com>]

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On Mon, Nov 14, 2011 at 07:10:28PM +0800, Jan Kara wrote:
> 
>   Hello,
> 
>   these two patches aim at making task waiting in balance_dirty_pages()
> killable.  This is desirable because otherwise if filesystem stops accepting
> writes (e.g. if device has been removed or other serious error condidion) we
> have a task stuck in D state forever.

Agreed totally. I myself has run into such conditions and get very
annoyed not being able to kill the hard throttled tasks -- they just
stuck there for ever if the error condition does not change.

>   I'm not sure who should merge these two patches... Al, Fengguang?

I'd like to do it -- otherwise there will obviously be merge conflicts.

Actually I also queued a patch to do this (attached). Your patches do
better on TASK_KILLABLE and the use of signal_pending() in write
routines, while mine goes further to add the break to various
filesystems.  How about combining them together?

Thanks,
Fengguang

[-- Attachment #2: writeback-break-on-signal-pending.patch --]
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Subject: writeback: quit throttling when fatal signal pending
Date: Wed Sep 08 17:40:22 CST 2010

This allows quick response to Ctrl-C etc. for impatient users.

It's necessary to abort the generic_perform_write() and other filesystem
write loops too, to avoid large write + SIGKILL combination exceeding
the dirty limit and possibly strange OOM.

It mainly helps the rare bdi/global dirty exceeded cases.
In the normal case of not exceeded, it will quit the loop anyway.

		if (fatal_signal_pending(current) &&
		    nr_reclaimable + nr_writeback <= dirty_thresh)
			break;

Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
cc: Chris Mason <chris.mason@oracle.com>
cc: Anton Altaparmakov <aia21@cantab.net>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 fs/btrfs/file.c       |    4 ++++
 fs/btrfs/ioctl.c      |    4 ++++
 fs/btrfs/relocation.c |    4 ++++
 fs/buffer.c           |    4 ++++
 fs/ntfs/attrib.c      |    2 ++
 fs/ntfs/file.c        |    6 ++++++
 mm/filemap.c          |    3 ++-
 mm/page-writeback.c   |    2 ++
 8 files changed, 28 insertions(+), 1 deletion(-)

--- linux-next.orig/mm/page-writeback.c	2011-11-13 20:37:11.000000000 +0800
+++ linux-next/mm/page-writeback.c	2011-11-13 20:37:57.000000000 +0800
@@ -1185,6 +1185,8 @@ pause:
 		 */
 		if (task_ratelimit)
 			break;
+		if (fatal_signal_pending(current))
+			break;
 	}
 
 	if (!dirty_exceeded && bdi->dirty_exceeded)
--- linux-next.orig/mm/filemap.c	2011-11-13 20:03:23.000000000 +0800
+++ linux-next/mm/filemap.c	2011-11-13 20:37:17.000000000 +0800
@@ -2463,7 +2463,8 @@ again:
 		written += copied;
 
 		balance_dirty_pages_ratelimited(mapping);
-
+		if (fatal_signal_pending(current))
+			break;
 	} while (iov_iter_count(i));
 
 	return written ? written : status;
--- linux-next.orig/fs/btrfs/file.c	2011-11-13 20:37:11.000000000 +0800
+++ linux-next/fs/btrfs/file.c	2011-11-13 20:37:17.000000000 +0800
@@ -1274,6 +1274,10 @@ static noinline ssize_t __btrfs_buffered
 						   dirty_pages);
 		if (dirty_pages < (root->leafsize >> PAGE_CACHE_SHIFT) + 1)
 			btrfs_btree_balance_dirty(root, 1);
+		if (fatal_signal_pending(current)) {
+			ret = -EINTR;
+			break;
+		}
 		btrfs_throttle(root);
 
 		pos += copied;
--- linux-next.orig/fs/btrfs/ioctl.c	2011-11-13 20:03:23.000000000 +0800
+++ linux-next/fs/btrfs/ioctl.c	2011-11-13 20:37:17.000000000 +0800
@@ -1115,6 +1115,10 @@ int btrfs_defrag_file(struct inode *inod
 
 		defrag_count += ret;
 		balance_dirty_pages_ratelimited_nr(inode->i_mapping, ret);
+		if (fatal_signal_pending(current)) {
+			ret = -EINTR;
+			goto out_ra;
+		}
 
 		if (newer_than) {
 			if (newer_off == (u64)-1)
--- linux-next.orig/fs/btrfs/relocation.c	2011-11-13 20:03:23.000000000 +0800
+++ linux-next/fs/btrfs/relocation.c	2011-11-13 20:37:17.000000000 +0800
@@ -3009,6 +3009,10 @@ static int relocate_file_extent_cluster(
 
 		index++;
 		balance_dirty_pages_ratelimited(inode->i_mapping);
+		if (fatal_signal_pending(current)) {
+			ret = -EINTR;
+			break;
+		}
 		btrfs_throttle(BTRFS_I(inode)->root);
 	}
 	WARN_ON(nr != cluster->nr);
--- linux-next.orig/fs/buffer.c	2011-11-13 20:03:23.000000000 +0800
+++ linux-next/fs/buffer.c	2011-11-13 20:37:17.000000000 +0800
@@ -2255,6 +2255,10 @@ static int cont_expand_zero(struct file 
 		err = 0;
 
 		balance_dirty_pages_ratelimited(mapping);
+		if (fatal_signal_pending(current)) {
+			err = -EINTR;
+			goto out;
+		}
 	}
 
 	/* page covers the boundary, find the boundary offset */
--- linux-next.orig/fs/ntfs/attrib.c	2011-11-13 20:03:23.000000000 +0800
+++ linux-next/fs/ntfs/attrib.c	2011-11-13 20:37:17.000000000 +0800
@@ -2588,6 +2588,8 @@ int ntfs_attr_set(ntfs_inode *ni, const 
 		unlock_page(page);
 		page_cache_release(page);
 		balance_dirty_pages_ratelimited(mapping);
+		if (fatal_signal_pending(current))
+			return -EINTR;
 		cond_resched();
 	}
 	/* If there is a last partial page, need to do it the slow way. */
--- linux-next.orig/fs/ntfs/file.c	2011-11-13 20:03:23.000000000 +0800
+++ linux-next/fs/ntfs/file.c	2011-11-13 20:37:17.000000000 +0800
@@ -278,6 +278,10 @@ do_non_resident_extend:
 		 * files.
 		 */
 		balance_dirty_pages_ratelimited(mapping);
+		if (fatal_signal_pending(current)) {
+			err = -EINTR;
+			goto init_err_out;
+		}
 		cond_resched();
 	} while (++index < end_index);
 	read_lock_irqsave(&ni->size_lock, flags);
@@ -2054,6 +2058,8 @@ static ssize_t ntfs_file_buffered_write(
 		if (unlikely(status))
 			break;
 		balance_dirty_pages_ratelimited(mapping);
+		if (fatal_signal_pending(current))
+			break;
 		cond_resched();
 	} while (count);
 err_out: