| 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
| ||
|
Message-ID: <5783072b-0341-dccb-8f07-c92230964d83@suse.cz>
Date: Tue, 21 Jun 2016 13:43:47 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: David Rientjes <rientjes@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>,
Hugh Dickins <hughd@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Minchan Kim <minchan@...nel.org>
Subject: Re: [patch] mm, compaction: abort free scanner if split fails
On 06/21/2016 12:27 AM, David Rientjes wrote:
> If the memory compaction free scanner cannot successfully split a free
> page (only possible due to per-zone low watermark), terminate the free
> scanner rather than continuing to scan memory needlessly.
>
> If the per-zone watermark is insufficient for a free page of
> order <= cc->order, then terminate the scanner since future splits will
> also likely fail.
>
> This prevents the compaction freeing scanner from scanning all memory on
> very large zones (very noticeable for zones > 128GB, for instance) when
> all splits will likely fail.
>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
But some notes below.
> ---
> mm/compaction.c | 49 +++++++++++++++++++++++++++++--------------------
> 1 file changed, 29 insertions(+), 20 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -494,24 +494,22 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>
> /* Found a free page, will break it into order-0 pages */
> order = page_order(page);
> - isolated = __isolate_free_page(page, page_order(page));
> + isolated = __isolate_free_page(page, order);
> + if (!isolated)
> + break;
This seems to fix as a side-effect a bug in Joonsoo's mmotm patch
mm-compaction-split-freepages-without-holding-the-zone-lock.patch, that
Minchan found: http://marc.info/?l=linux-mm&m=146607176528495&w=2
So it should be noted somewhere so they are merged together. Or Joonsoo
posts an isolated fix and this patch has to rebase.
> set_page_private(page, order);
> total_isolated += isolated;
> list_add_tail(&page->lru, freelist);
>
> - /* If a page was split, advance to the end of it */
> - if (isolated) {
> - cc->nr_freepages += isolated;
> - if (!strict &&
> - cc->nr_migratepages <= cc->nr_freepages) {
> - blockpfn += isolated;
> - break;
> - }
> -
> - blockpfn += isolated - 1;
> - cursor += isolated - 1;
> - continue;
> + /* Advance to the end of split page */
> + cc->nr_freepages += isolated;
> + if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
> + blockpfn += isolated;
> + break;
> }
> + blockpfn += isolated - 1;
> + cursor += isolated - 1;
> + continue;
>
> isolate_fail:
> if (strict)
> @@ -521,6 +519,9 @@ isolate_fail:
>
> }
>
> + if (locked)
> + spin_unlock_irqrestore(&cc->zone->lock, flags);
> +
> /*
> * There is a tiny chance that we have read bogus compound_order(),
> * so be careful to not go outside of the pageblock.
> @@ -542,9 +543,6 @@ isolate_fail:
> if (strict && blockpfn < end_pfn)
> total_isolated = 0;
>
> - if (locked)
> - spin_unlock_irqrestore(&cc->zone->lock, flags);
> -
> /* Update the pageblock-skip if the whole pageblock was scanned */
> if (blockpfn == end_pfn)
> update_pageblock_skip(cc, valid_page, total_isolated, false);
> @@ -622,7 +620,7 @@ isolate_freepages_range(struct compact_control *cc,
> */
> }
>
> - /* split_free_page does not map the pages */
> + /* __isolate_free_page() does not map the pages */
> map_pages(&freelist);
>
> if (pfn < end_pfn) {
> @@ -1071,6 +1069,7 @@ static void isolate_freepages(struct compact_control *cc)
> block_end_pfn = block_start_pfn,
> block_start_pfn -= pageblock_nr_pages,
> isolate_start_pfn = block_start_pfn) {
> + unsigned long isolated;
>
> /*
> * This can iterate a massively long zone without finding any
> @@ -1095,8 +1094,12 @@ static void isolate_freepages(struct compact_control *cc)
> continue;
>
> /* Found a block suitable for isolating free pages from. */
> - isolate_freepages_block(cc, &isolate_start_pfn,
> - block_end_pfn, freelist, false);
> + isolated = isolate_freepages_block(cc, &isolate_start_pfn,
> + block_end_pfn, freelist, false);
> + /* If free page split failed, do not continue needlessly */
More accurately, free page isolation failed?
> + if (!isolated && isolate_start_pfn < block_end_pfn &&
> + cc->nr_freepages <= cc->nr_migratepages)
> + break;
>
> /*
> * If we isolated enough freepages, or aborted due to async
> @@ -1124,7 +1127,7 @@ static void isolate_freepages(struct compact_control *cc)
> }
> }
>
> - /* split_free_page does not map the pages */
> + /* __isolate_free_page() does not map the pages */
> map_pages(freelist);
>
> /*
> @@ -1703,6 +1706,12 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
> continue;
> }
>
> + /* Don't attempt compaction if splitting free page will fail */
> + if (!zone_watermark_ok(zone, 0,
> + low_wmark_pages(zone) + (1 << order),
> + 0, 0))
> + continue;
> +
Please don't add this, compact_zone already checks this via
compaction_suitable() (and the usual 2 << order gap), so this is adding
yet another watermark check with a different kind of gap.
Thanks.
> status = compact_zone_order(zone, order, gfp_mask, mode,
> &zone_contended, alloc_flags,
> ac_classzone_idx(ac));
>
Powered by blists - more mailing lists