linux-kernel - Re: [PATCH 2/2] tmpfs: fix mempolicy object leaks

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Message-ID: <alpine.LNX.2.00.1303051101350.27525@eggly.anvils>
Date:	Tue, 5 Mar 2013 11:40:39 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Will Huck <will.huckk@...il.com>
cc:	Greg Thelen <gthelen@...gle.com>, akpm@...ux-foundation.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] tmpfs: fix mempolicy object leaks

On Mon, 4 Mar 2013, Will Huck wrote:
> 
> Could you explain me why shmem has more relationship with mempolicy? It seems
> that there are many codes in shmem handle mempolicy, but other components in
> mm subsystem just have little.

NUMA mempolicy is mostly handled in mm/mempolicy.c, which services the
mbind, migrate_pages, set_mempolicy, get_mempolicy system calls: which
govern how process memory is distributed across NUMA nodes.

mm/shmem.c is affected because it was also found useful to specify
mempolicy on the shared memory objects which may back process memory:
that includes SysV SHM and POSIX shared memory and tmpfs.  mm/hugetlb.c
contains some mempolicy handling for hugetlbfs; fs/ramfs is kept minimal,
so nothing in there.

Those are the memory-based filesystems, where NUMA mempolicy is most
natural.  The regular filesystems could support shared mempolicy too,
but that would raise more awkward design questions.

Hugh
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