lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20140203095329.GH6732@suse.de>
Date:	Mon, 3 Feb 2014 09:53:29 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch] mm, compaction: avoid isolating pinned pages

On Sat, Feb 01, 2014 at 09:46:26PM -0800, David Rientjes wrote:
> Page migration will fail for memory that is pinned in memory with, for
> example, get_user_pages().  In this case, it is unnecessary to take
> zone->lru_lock or isolating the page and passing it to page migration
> which will ultimately fail.
> 
> This is a racy check, the page can still change from under us, but in
> that case we'll just fail later when attempting to move the page.
> 
> This avoids very expensive memory compaction when faulting transparent
> hugepages after pinning a lot of memory with a Mellanox driver.
> 
> On a 128GB machine and pinning ~120GB of memory, before this patch we
> see the enormous disparity in the number of page migration failures
> because of the pinning (from /proc/vmstat):
> 
> compact_blocks_moved 7609
> compact_pages_moved 3431
> compact_pagemigrate_failed 133219
> compact_stall 13
> 
> After the patch, it is much more efficient:
> 
> compact_blocks_moved 7998
> compact_pages_moved 6403
> compact_pagemigrate_failed 3
> compact_stall 15
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  mm/compaction.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -578,6 +578,14 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
>  			continue;
>  		}
>  
> +		/*
> +		 * Migration will fail if an anonymous page is pinned in memory,
> +		 * so avoid taking zone->lru_lock and isolating it unnecessarily
> +		 * in an admittedly racy check.
> +		 */
> +		if (!page_mapping(page) && page_count(page))
> +			continue;
> +

Are you sure about this? The page_count check migration does is this

        int expected_count = 1 + extra_count;
        if (!mapping) {
                if (page_count(page) != expected_count)
                        return -EAGAIN;
                return MIGRATEPAGE_SUCCESS;
        }

        spin_lock_irq(&mapping->tree_lock);

        pslot = radix_tree_lookup_slot(&mapping->page_tree,
                                        page_index(page));

        expected_count += 1 + page_has_private(page);

Migration expects and can migrate pages with no mapping and a page count
but you are now skipping them. I think you may have intended to split
migrations page count into a helper or copy the logic.

-- 
Mel Gorman
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ