linux-kernel - Re: [PATCH v1] mm/madvise: update comment on sys

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Message-ID: <20160127152835.GD13956@dhcp22.suse.cz>
Date:	Wed, 27 Jan 2016 16:28:35 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Jason Baron <jbaron@...hat.com>,
	Chen Gong <gong.chen@...ux.intel.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH v1] mm/madvise: update comment on sys_madvise()

On Wed 27-01-16 10:24:25, Naoya Horiguchi wrote:
> Some new MADV_* advices are not documented in sys_madvise() comment.
> So let's update it.
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>

Other than few suggestions below
Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/madvise.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git v4.4-mmotm-2016-01-20-16-10/mm/madvise.c v4.4-mmotm-2016-01-20-16-10_patched/mm/madvise.c
> index 6a77114..c897b15 100644
> --- v4.4-mmotm-2016-01-20-16-10/mm/madvise.c
> +++ v4.4-mmotm-2016-01-20-16-10_patched/mm/madvise.c
> @@ -639,14 +639,26 @@ madvise_behavior_valid(int behavior)
>   *		some pages ahead.
>   *  MADV_DONTNEED - the application is finished with the given range,
>   *		so the kernel can free resources associated with it.
> + *  MADV_FREE - the application marks pages in the given range as lasyfree,

s@...yfree@...y free@

> + *		where actual purges are postponed until memory pressure happens.
>   *  MADV_REMOVE - the application wants to free up the given range of
>   *		pages and associated backing store.
>   *  MADV_DONTFORK - omit this area from child's address space when forking:
>   *		typically, to avoid COWing pages pinned by get_user_pages().
>   *  MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
> + *  MADV_HWPOISON - trigger memory error handler as if the given memory range
> + *		were corrupted by unrecoverable hardware memory failure.
> + *  MADV_SOFT_OFFLINE - try to soft-offline the given range of memory.
>   *  MADV_MERGEABLE - the application recommends that KSM try to merge pages in
>   *		this area with pages of identical content from other such areas.
>   *  MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.
> + *  MADV_HUGEPAGE - the application wants to allocate transparent hugepages to
> + *		load the content of the given memory range.

I guess that a slightly different wording would be better:

application wants to back the given range by transparent huge pages in
the future. Existing pages might be coalesced and new pages might be
allocated as THP.

> + *  MADV_NOHUGEPAGE - cancel MADV_HUGEPAGE: no longer allocate transparent
> + *		hugepages.

Mark the given range as not worth being backed by transparent huge pages
so neither existing pages will be coalesced into THP nor new pages will
be allocated as THP.

> + *  MADV_DONTDUMP - the application wants to prevent pages in the given range
> + *		from being included in its core dump.
> + *  MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.
>   *
>   * return values:
>   *  zero    - success
> -- 
> 2.7.0
> 
> --
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-- 
Michal Hocko
SUSE Labs