* Re: Question about __zone_watermark_ok: why there is a "+ 1" in computing free_pages?
[not found] <CAKXJSOHu+sQ1NeMsRvFyp2GYoB6g+50boUu=-QvbxxjcqgOAVA@mail.gmail.com>
@ 2011-12-05 16:14 ` Michal Hocko
2011-12-05 17:06 ` Mel Gorman
2011-12-08 16:24 ` KOSAKI Motohiro
0 siblings, 2 replies; 3+ messages in thread
From: Michal Hocko @ 2011-12-05 16:14 UTC (permalink / raw)
To: Wang Sheng-Hui; +Cc: linux-mm, linux-kernel, Mel Gorman, Andrew Morton
On Fri 25-11-11 09:21:35, Wang Sheng-Hui wrote:
> In line 1459, we have "free_pages -= (1 << order) + 1;".
> Suppose allocating one 0-order page, here we'll get
> free_pages -= 1 + 1
> I wonder why there is a "+ 1"?
Good spot. Check the patch bellow.
---
>From 38a1cf351b111e8791d2db538c8b0b912f5df8b8 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.cz>
Date: Mon, 5 Dec 2011 17:04:23 +0100
Subject: [PATCH] mm: fix off-by-two in __zone_watermark_ok
88f5acf8 [mm: page allocator: adjust the per-cpu counter threshold when
memory is low] changed the form how free_pages is calculated but it
forgot that we used to do free_pages - ((1 << order) - 1) so we ended up
with off-by-two when calculating free_pages.
Spotted-by: Wang Sheng-Hui <shhuiw@gmail.com>
Signed-off-by: Michal Hocko <mhocko@suse.cz>
---
mm/page_alloc.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9dd443d..8a2f1b6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1457,7 +1457,7 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark,
long min = mark;
int o;
- free_pages -= (1 << order) + 1;
+ free_pages -= (1 << order) - 1;
if (alloc_flags & ALLOC_HIGH)
min -= min / 2;
if (alloc_flags & ALLOC_HARDER)
--
1.7.7.3
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: Question about __zone_watermark_ok: why there is a "+ 1" in computing free_pages?
2011-12-05 16:14 ` Question about __zone_watermark_ok: why there is a "+ 1" in computing free_pages? Michal Hocko
@ 2011-12-05 17:06 ` Mel Gorman
2011-12-08 16:24 ` KOSAKI Motohiro
1 sibling, 0 replies; 3+ messages in thread
From: Mel Gorman @ 2011-12-05 17:06 UTC (permalink / raw)
To: Michal Hocko; +Cc: Wang Sheng-Hui, linux-mm, linux-kernel, Andrew Morton
On Mon, Dec 05, 2011 at 05:14:43PM +0100, Michal Hocko wrote:
> From 38a1cf351b111e8791d2db538c8b0b912f5df8b8 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.cz>
> Date: Mon, 5 Dec 2011 17:04:23 +0100
> Subject: [PATCH] mm: fix off-by-two in __zone_watermark_ok
>
> 88f5acf8 [mm: page allocator: adjust the per-cpu counter threshold when
> memory is low] changed the form how free_pages is calculated but it
> forgot that we used to do free_pages - ((1 << order) - 1) so we ended up
> with off-by-two when calculating free_pages.
>
> Spotted-by: Wang Sheng-Hui <shhuiw@gmail.com>
> Signed-off-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Mel Gorman <mgorman@suse.de>
--
Mel Gorman
SUSE Labs
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Question about __zone_watermark_ok: why there is a "+ 1" in computing free_pages?
2011-12-05 16:14 ` Question about __zone_watermark_ok: why there is a "+ 1" in computing free_pages? Michal Hocko
2011-12-05 17:06 ` Mel Gorman
@ 2011-12-08 16:24 ` KOSAKI Motohiro
1 sibling, 0 replies; 3+ messages in thread
From: KOSAKI Motohiro @ 2011-12-08 16:24 UTC (permalink / raw)
To: Michal Hocko
Cc: Wang Sheng-Hui, linux-mm, linux-kernel, Mel Gorman, Andrew Morton
(12/5/11 11:14 AM), Michal Hocko wrote:
> On Fri 25-11-11 09:21:35, Wang Sheng-Hui wrote:
>> In line 1459, we have "free_pages -= (1<< order) + 1;".
>> Suppose allocating one 0-order page, here we'll get
>> free_pages -= 1 + 1
>> I wonder why there is a "+ 1"?
>
> Good spot. Check the patch bellow.
> ---
> From 38a1cf351b111e8791d2db538c8b0b912f5df8b8 Mon Sep 17 00:00:00 2001
> From: Michal Hocko<mhocko@suse.cz>
> Date: Mon, 5 Dec 2011 17:04:23 +0100
> Subject: [PATCH] mm: fix off-by-two in __zone_watermark_ok
>
> 88f5acf8 [mm: page allocator: adjust the per-cpu counter threshold when
> memory is low] changed the form how free_pages is calculated but it
> forgot that we used to do free_pages - ((1<< order) - 1) so we ended up
> with off-by-two when calculating free_pages.
>
> Spotted-by: Wang Sheng-Hui<shhuiw@gmail.com>
> Signed-off-by: Michal Hocko<mhocko@suse.cz>
> ---
> mm/page_alloc.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9dd443d..8a2f1b6 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1457,7 +1457,7 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark,
> long min = mark;
> int o;
>
> - free_pages -= (1<< order) + 1;
> + free_pages -= (1<< order) - 1;
> if (alloc_flags& ALLOC_HIGH)
> min -= min / 2;
> if (alloc_flags& ALLOC_HARDER)
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2011-12-08 16:24 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
[not found] <CAKXJSOHu+sQ1NeMsRvFyp2GYoB6g+50boUu=-QvbxxjcqgOAVA@mail.gmail.com>
2011-12-05 16:14 ` Question about __zone_watermark_ok: why there is a "+ 1" in computing free_pages? Michal Hocko
2011-12-05 17:06 ` Mel Gorman
2011-12-08 16:24 ` KOSAKI Motohiro
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).