linux-kernel - Re: [PATCH] mm,migration: Avoid race between shift_arg_pages() and rmap_walk() during migration by not migrating temporary stacks

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Date:	Wed, 12 May 2010 16:33:12 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] mm,migration: Avoid race between shift_arg_pages() and
 rmap_walk() during migration by not migrating temporary stacks


Still think this special casing is not that good.

One can also disable migration by providing a migration function that
always fails. One such function exists in mm/migrate.c:

/* Always fail migration. Used for mappings that are not movable */
int fail_migrate_page(struct address_space *mapping,
                        struct page *newpage, struct page *page)
{
        return -EIO;
}
EXPORT_SYMBOL(fail_migrate_page);


The migration function is specified in

vma->vm_ops->migrate

If that is set to fail_migrate_page() then the pages in the vma will never
be migrated. XFS uses it f.e. to avoid page migration:

STATIC int
xfs_mapping_buftarg(
        xfs_buftarg_t           *btp,
        struct block_device     *bdev)
{
        struct backing_dev_info *bdi;
        struct inode            *inode;
        struct address_space    *mapping;
        static const struct address_space_operations mapping_aops = {
                .sync_page = block_sync_page,
                .migratepage = fail_migrate_page,
        };



Would it not be possible to do something similar for the temporary stack?
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