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From: Mike Kravetz <mike.kravetz@oracle.com>
To: Li Xinhai <lixinhai.lxh@gmail.com>, linux-mm@kvack.org
Cc: akpm@linux-foundation.org, Michal Hocko <mhocko@suse.com>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	linux-man <linux-man@vger.kernel.org>
Subject: Re: [PATCH v2] mm/mempolicy: support MPOL_MF_STRICT for huge page mapping
Date: Thu, 13 Feb 2020 08:17:00 -0800
Message-ID: <ae20284f-5a1e-0668-f299-0edcd445e487@oracle.com> (raw)
In-Reply-To: <1581559627-6206-1-git-send-email-lixinhai.lxh@gmail.com>

On 2/12/20 6:07 PM, Li Xinhai wrote:
> MPOL_MF_STRICT is used in mbind() for purposes:
> (1) MPOL_MF_STRICT is set alone without MPOL_MF_MOVE or MPOL_MF_MOVE_ALL,
>     to check if there is misplaced page and return -EIO;
> (2) MPOL_MF_STRICT is set with MPOL_MF_MOVE or MPOL_MF_MOVE_ALL, to check
>     if there is misplaced page which is failed to isolate, or page is
>     success on isolate but failed to move, and return -EIO.
> 
> For non hugepage mapping, (1) and (2) are implemented as expectation.
> For hugepage mapping, (1) is not implemented. And in (2), the part about
> failed to isolate and report -EIO is not implemented.
> 
> This patch implements the missed parts for hugepage mapping. Benefits
> with it applied:
> - User space can apply same code logic to handle mbind() on hugepage and
>   non hugepage mapping;
> - Reliably using MPOL_MF_STRICT alone to check whether there is misplaced
>   page or not when bind policy on address range, especially for address
>   range which contains both hugepage and non hugepage mapping.
> 
> Analysis of potential impact to existing users:
> - If MPOL_MF_STRICT alone was previously used, hugetlb pages not following
>   the memory policy would not cause an EIO error.  After this change,
>   hugetlb pages are treated like all other pages. If  MPOL_MF_STRICT alone
>   is used and hugetlb pages do not follow memory policy an EIO error will
>   be returned.
> - For users who using MPOL_MF_STRICT with MPOL_MF_MOVE or
>   MPOL_MF_MOVE_ALL, the semantic about some pages could not be moved will
>   not be changed by this patch, because failed to isolate and failed to
>   move have same effects to users, so their existing code will not be
>   impacted.
> 
> In mbind man page, the note about 'MPOL_MF_STRICT is ignored on huge page
> mappings' can be removed after this patch is applied.
> 
> Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: linux-man <linux-man@vger.kernel.org>

Thanks for the update.

The current behavior with MPOL_MF_STRICT and hugetlb pages is inconsistent
and does not match documentation (as described above).  The special behavior
for hugetlb pages ideally should have been removed when hugetlb page migration
was introduced.  It is unlikely that anyone relies on today's inconsistent
behavior, and removing one more case of special handling for hugetlb pages
is a good thing.

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
-- 
Mike Kravetz

  reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-13  2:07 Li Xinhai
2020-02-13 16:17 ` Mike Kravetz [this message]
2020-02-14  3:36 ` HORIGUCHI NAOYA(堀口 直也)

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