[BUGFIX take 2] [PATCH] write-back: fix nr_to_write counter

[BUGFIX take 2] [PATCH] write-back: fix nr_to_write counter

[Artem Bityutskiy]

From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Date: Mon, 2 Feb 2009 18:33:49 +0200
Subject: [PATCH] write-back: fix nr_to_write counter

Commit 05fe478dd04e02fa230c305ab9b5616669821dd3 introduced some
@wbc->nr_to_write breakage. Here is the change from the commit:

--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -963,8 +963,10 @@ retry:
                                }
                        }

-                       if (--nr_to_write <= 0)
-                               done = 1;
+                       if (wbc->sync_mode == WB_SYNC_NONE) {
+                               if (--wbc->nr_to_write <= 0)
+                                       done = 1;
+                       }
                        if (wbc->nonblocking && bdi_write_congested(bdi)) {
                                wbc->encountered_congestion = 1;
                                done = 1
                        }

It makes the following changes:
1. Decrement wbc->nr_to_write instead of nr_to_write
2. Decrement wbc->nr_to_write _only_ if wbc->sync_mode == WB_SYNC_NONE
3. If synced nr_to_write pages, stop only if if wbc->sync_mode ==
WB_SYNC_NONE, otherwise keep going.

However, according to the commit message, the intention was to
only make change 3. Change 1 is a bug. Change 2 does not seem to be
necessary, and it breaks UBIFS expectations, so if needed, it
should be done separately later. And change 2 does not seem to
be documented in the commit message.

This patch des the following:
1. Undo changes 1 and 2
2. Add a comment explaining change 3 (it very useful to have comments in
_code_, not only in the commit).

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 mm/page-writeback.c |   21 +++++++++++++++------
 1 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b493db7..13a2b8e 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1051,13 +1051,22 @@ continue_unlock:
 				}
  			}
 
-			if (wbc->sync_mode == WB_SYNC_NONE) {
-				wbc->nr_to_write--;
-				if (wbc->nr_to_write <= 0) {
-					done = 1;
-					break;
-				}
+			if (nr_to_write > 0)
+				nr_to_write--;
+			else if (wbc->sync_mode == WB_SYNC_NONE) {
+				/*
+				 * We stop writing back only if we are not
+				 * doing integrity sync. In case of integrity
+				 * sync we have to keep going because someone
+				 * may be concurrently dirtying pages, and we
+				 * might have synced a lot of newly appeared
+				 * dirty pages, bud have not synced all of the
+				 * old dirty pages.
+				 */
+				done = 1;
+				break;
 			}
+
 			if (wbc->nonblocking && bdi_write_congested(bdi)) {
 				wbc->encountered_congestion = 1;
 				done = 1;
-- 
1.6.0.6


-- 
Best regards,
Artem Bityutskiy (Битюцкий Артём)

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Re: [BUGFIX take 2] [PATCH] write-back: fix nr_to_write counter

[Dave Kleikamp]

On Tue, 2009-02-03 at 12:08 +0200, Artem Bityutskiy wrote:
> From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
> Date: Mon, 2 Feb 2009 18:33:49 +0200
> Subject: [PATCH] write-back: fix nr_to_write counter
> 
> Commit 05fe478dd04e02fa230c305ab9b5616669821dd3 introduced some
> @wbc->nr_to_write breakage. Here is the change from the commit:
> 
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -963,8 +963,10 @@ retry:
>                                 }
>                         }
> 
> -                       if (--nr_to_write <= 0)
> -                               done = 1;
> +                       if (wbc->sync_mode == WB_SYNC_NONE) {
> +                               if (--wbc->nr_to_write <= 0)
> +                                       done = 1;
> +                       }
>                         if (wbc->nonblocking && bdi_write_congested(bdi)) {
>                                 wbc->encountered_congestion = 1;
>                                 done = 1
>                         }

Actually quoting a patch in the description in this manner will make the
patch fail to apply (or fail to apply correctly).  If you must quote the
patch, you should probably prepend ">" or something.

> It makes the following changes:
> 1. Decrement wbc->nr_to_write instead of nr_to_write
> 2. Decrement wbc->nr_to_write _only_ if wbc->sync_mode == WB_SYNC_NONE
> 3. If synced nr_to_write pages, stop only if if wbc->sync_mode ==
> WB_SYNC_NONE, otherwise keep going.
> 
> However, according to the commit message, the intention was to
> only make change 3. Change 1 is a bug. Change 2 does not seem to be
> necessary, and it breaks UBIFS expectations, so if needed, it
> should be done separately later. And change 2 does not seem to
> be documented in the commit message.
> 
> This patch des the following:
> 1. Undo changes 1 and 2
> 2. Add a comment explaining change 3 (it very useful to have comments in
> _code_, not only in the commit).
> 
> Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
> Acked-by: Nick Piggin <npiggin@suse.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
>  mm/page-writeback.c |   21 +++++++++++++++------
>  1 files changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index b493db7..13a2b8e 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1051,13 +1051,22 @@ continue_unlock:
>  				}
>   			}
> 
> -			if (wbc->sync_mode == WB_SYNC_NONE) {
> -				wbc->nr_to_write--;
> -				if (wbc->nr_to_write <= 0) {
> -					done = 1;
> -					break;
> -				}
> +			if (nr_to_write > 0)
> +				nr_to_write--;
> +			else if (wbc->sync_mode == WB_SYNC_NONE) {
> +				/*
> +				 * We stop writing back only if we are not
> +				 * doing integrity sync. In case of integrity
> +				 * sync we have to keep going because someone
> +				 * may be concurrently dirtying pages, and we
> +				 * might have synced a lot of newly appeared
> +				 * dirty pages, bud have not synced all of the
> +				 * old dirty pages.
> +				 */
> +				done = 1;
> +				break;
>  			}
> +
>  			if (wbc->nonblocking && bdi_write_congested(bdi)) {
>  				wbc->encountered_congestion = 1;
>  				done = 1;
> -- 
> 1.6.0.6
> 
> 
-- 
David Kleikamp
IBM Linux Technology Center

Re: [BUGFIX take 3] [PATCH] write-back: fix nr_to_write counter

[Artem Bityutskiy]

[Take into account Dave Kleikamp's suggestion and fix commit message]

From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Date: Mon, 2 Feb 2009 18:33:49 +0200
Subject: [PATCH] write-back: fix nr_to_write counter

Commit 05fe478dd04e02fa230c305ab9b5616669821dd3 introduced some
@wbc->nr_to_write breakage. Here is the change from the commit:

>--- a/mm/page-writeback.c
>+++ b/mm/page-writeback.c
>@@ -963,8 +963,10 @@ retry:
>                               }
>                       }
>
>                       if (--nr_to_write <= 0)
>                               done = 1;
>                       if (wbc->sync_mode == WB_SYNC_NONE) {
>                               if (--wbc->nr_to_write <= 0)
>                                       done = 1;
>                       }
>                       if (wbc->nonblocking && bdi_write_congested(bdi)) {
>                               wbc->encountered_congestion = 1;
>                               done = 1
>                       }

It makes the following changes:
1. Decrement wbc->nr_to_write instead of nr_to_write
2. Decrement wbc->nr_to_write _only_ if wbc->sync_mode == WB_SYNC_NONE
3. If synced nr_to_write pages, stop only if if wbc->sync_mode ==
WB_SYNC_NONE, otherwise keep going.

However, according to the commit message, the intention was to
only make change 3. Change 1 is a bug. Change 2 does not seem to be
necessary, and it breaks UBIFS expectations, so if needed, it
should be done separately later. And change 2 does not seem to
be documented in the commit message.

This patch does the following:
1. Undo changes 1 and 2
2. Add a comment explaining change 3 (it very useful to have comments in
_code_, not only in the commit).

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 mm/page-writeback.c |   21 +++++++++++++++------
 1 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b493db7..13a2b8e 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1051,13 +1051,22 @@ continue_unlock:
 				}
  			}
 
-			if (wbc->sync_mode == WB_SYNC_NONE) {
-				wbc->nr_to_write--;
-				if (wbc->nr_to_write <= 0) {
-					done = 1;
-					break;
-				}
+			if (nr_to_write > 0)
+				nr_to_write--;
+			else if (wbc->sync_mode == WB_SYNC_NONE) {
+				/*
+				 * We stop writing back only if we are not
+				 * doing integrity sync. In case of integrity
+				 * sync we have to keep going because someone
+				 * may be concurrently dirtying pages, and we
+				 * might have synced a lot of newly appeared
+				 * dirty pages, bud have not synced all of the
+				 * old dirty pages.
+				 */
+				done = 1;
+				break;
 			}
+
 			if (wbc->nonblocking && bdi_write_congested(bdi)) {
 				wbc->encountered_congestion = 1;
 				done = 1;
-- 
1.6.0.6


-- 
Best regards,
Artem Bityutskiy (Битюцкий Артём)

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[BUGFIX take 4] [PATCH] write-back: fix nr_to_write counter

[Artem Bityutskiy]

[Fix spelling, pointed to by jim owens]

From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Date: Mon, 2 Feb 2009 18:33:49 +0200
Subject: [PATCH] write-back: fix nr_to_write counter

Commit 05fe478dd04e02fa230c305ab9b5616669821dd3 introduced some
@wbc->nr_to_write breakage. Here is the change from the commit:

>--- a/mm/page-writeback.c
>+++ b/mm/page-writeback.c
>@@ -963,8 +963,10 @@ retry:
>                               }
>                       }
>
>                       if (--nr_to_write <= 0)
>                               done = 1;
>                       if (wbc->sync_mode == WB_SYNC_NONE) {
>                               if (--wbc->nr_to_write <= 0)
>                                       done = 1;
>                       }
>                       if (wbc->nonblocking && bdi_write_congested(bdi)) {
>                               wbc->encountered_congestion = 1;
>                               done = 1
>                       }

It makes the following changes:
1. Decrement wbc->nr_to_write instead of nr_to_write
2. Decrement wbc->nr_to_write _only_ if wbc->sync_mode == WB_SYNC_NONE
3. If synced nr_to_write pages, stop only if if wbc->sync_mode ==
WB_SYNC_NONE, otherwise keep going.

However, according to the commit message, the intention was to
only make change 3. Change 1 is a bug. Change 2 does not seem to be
necessary, and it breaks UBIFS expectations, so if needed, it
should be done separately later. And change 2 does not seem to
be documented in the commit message.

This patch does the following:
1. Undo changes 1 and 2
2. Add a comment explaining change 3 (it very useful to have comments in
_code_, not only in the commit).

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 mm/page-writeback.c |   21 +++++++++++++++------
 1 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b493db7..dc32dae 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1051,13 +1051,22 @@ continue_unlock:
 				}
  			}
 
-			if (wbc->sync_mode == WB_SYNC_NONE) {
-				wbc->nr_to_write--;
-				if (wbc->nr_to_write <= 0) {
-					done = 1;
-					break;
-				}
+			if (nr_to_write > 0)
+				nr_to_write--;
+			else if (wbc->sync_mode == WB_SYNC_NONE) {
+				/*
+				 * We stop writing back only if we are not
+				 * doing integrity sync. In case of integrity
+				 * sync we have to keep going because someone
+				 * may be concurrently dirtying pages, and we
+				 * might have synced a lot of newly appeared
+				 * dirty pages, but have not synced all of the
+				 * old dirty pages.
+				 */
+				done = 1;
+				break;
 			}
+
 			if (wbc->nonblocking && bdi_write_congested(bdi)) {
 				wbc->encountered_congestion = 1;
 				done = 1;
-- 
1.6.0.6

-- 
Best regards,
Artem Bityutskiy (Битюцкий Артём)