linux-kernel - Re: [PATCH v17 1/7] mm: support madvise(MADV

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Message-ID: <20141127144725.GB19157@dhcp22.suse.cz>
Date:	Thu, 27 Nov 2014 15:47:25 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Michael Kerrisk <mtk.manpages@...il.com>,
	linux-api@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Jason Evans <je@...com>,
	zhangyanfei@...fujitsu.com,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v17 1/7] mm: support madvise(MADV_FREE)

[Late but I didn't get to this soone - I hope this is still up-to-date
version]

On Mon 20-10-14 19:11:58, Minchan Kim wrote:
> Linux doesn't have an ability to free pages lazy while other OS
> already have been supported that named by madvise(MADV_FREE).
> 
> The gain is clear that kernel can discard freed pages rather than
> swapping out or OOM if memory pressure happens.
> 
> Without memory pressure, freed pages would be reused by userspace
> without another additional overhead(ex, page fault + allocation
> + zeroing).
> 
> How to work is following as.
> 
> When madvise syscall is called, VM clears dirty bit of ptes of
> the range. If memory pressure happens, VM checks dirty bit of
> page table and if it found still "clean", it means it's a
> "lazyfree pages" so VM could discard the page instead of swapping out.
> Once there was store operation for the page before VM peek a page
> to reclaim, dirty bit is set so VM can swap out the page instead of
> discarding.

Is there any patch for madvise man page? I guess the semantic will be
same/similar to FreeBSD:
http://www.freebsd.org/cgi/man.cgi?query=madvise&sektion=2

I guess the changelog should be more specific that this is only for the
private MAP_ANON mappings (same applies to the patch for man).

> Firstly, heavy users would be general allocators(ex, jemalloc,
> tcmalloc and hope glibc supports it) and jemalloc/tcmalloc already
> have supported the feature for other OS(ex, FreeBSD)
> 
[...]
> 
> Cc: Michael Kerrisk <mtk.manpages@...il.com>
> Cc: Linux API <linux-api@...r.kernel.org>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Jason Evans <je@...com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Acked-by: Zhang Yanfei <zhangyanfei@...fujitsu.com>
> Acked-by: Rik van Riel <riel@...hat.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>

Reviewed-by: Michal Hocko <mhocko@...e.cz>
[...]
-- 
Michal Hocko
SUSE Labs
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