mm: consider compaction feedback also for costly allocation
PAGE_ALLOC_COSTLY_ORDER retry logic is mostly handled inside should_reclaim_retry currently where we decide to not retry after at least order worth of pages were reclaimed or the watermark check for at least one zone would succeed after reclaiming all pages if the reclaim hasn't made any progress. Compaction feedback is mostly ignored and we just try to make sure that the compaction did at least something before giving up. The first condition was added by a41f24ea ("page allocator: smarter retry of costly-order allocations) and it assumed that lumpy reclaim could have created a page of the sufficient order. Lumpy reclaim, has been removed quite some time ago so the assumption doesn't hold anymore. Remove the check for the number of reclaimed pages and rely on the compaction feedback solely. should_reclaim_retry now only makes sure that we keep retrying reclaim for high order pages only if they are hidden by watermaks so order-0 reclaim makes really sense. should_compact_retry now keeps retrying even for the costly allocations. The number of retries is reduced wrt. !costly requests because they are less important and harder to grant and so their pressure shouldn't cause contention for other requests or cause an over reclaim. We also do not reset no_progress_loops for costly request to make sure we do not keep reclaiming too agressively. This has been tested by running a process which fragments memory: - compact memory - mmap large portion of the memory (1920M on 2GRAM machine with 2G of swapspace) - MADV_DONTNEED single page in PAGE_SIZE*((1UL<<MAX_ORDER)-1) steps until certain amount of memory is freed (250M in my test) and reduce the step to (step / 2) + 1 after reaching the end of the mapping - then run a script which populates the page cache 2G (MemTotal) from /dev/zero to a new file And then tries to allocate nr_hugepages=$(awk '/MemAvailable/{printf "%d\n", $2/(2*1024)}' /proc/meminfo) huge pages. root@test1:~# echo 1 > /proc/sys/vm/overcommit_memory;echo 1 > /proc/sys/vm/compact_memory; ./fragment-mem-and-run /root/alloc_hugepages.sh 1920M 250M Node 0, zone DMA 31 28 31 10 2 0 2 1 2 3 1 Node 0, zone DMA32 437 319 171 50 28 25 20 16 16 14 437 * This is the /proc/buddyinfo after the compaction Done fragmenting. size=2013265920 freed=262144000 Node 0, zone DMA 165 48 3 1 2 0 2 2 2 2 0 Node 0, zone DMA32 35109 14575 185 51 41 12 6 0 0 0 0 * /proc/buddyinfo after memory got fragmented Executing "/root/alloc_hugepages.sh" Eating some pagecache 508623+0 records in 508623+0 records out 2083319808 bytes (2.1 GB) copied, 11.7292 s, 178 MB/s Node 0, zone DMA 3 5 3 1 2 0 2 2 2 2 0 Node 0, zone DMA32 111 344 153 20 24 10 3 0 0 0 0 * /proc/buddyinfo after page cache got eaten Trying to allocate 129 129 * 129 hugepages requested and all of them granted. Node 0, zone DMA 3 5 3 1 2 0 2 2 2 2 0 Node 0, zone DMA32 127 97 30 99 11 6 2 1 4 0 0 * /proc/buddyinfo after hugetlb allocation. 10 runs will behave as follows: Trying to allocate 130 130 -- Trying to allocate 129 129 -- Trying to allocate 128 128 -- Trying to allocate 129 129 -- Trying to allocate 128 128 -- Trying to allocate 129 129 -- Trying to allocate 132 132 -- Trying to allocate 129 129 -- Trying to allocate 128 128 -- Trying to allocate 129 129 So basically 100% success for all 10 attempts. Without the patch numbers looked much worse: Trying to allocate 128 12 -- Trying to allocate 129 14 -- Trying to allocate 129 7 -- Trying to allocate 129 16 -- Trying to allocate 129 30 -- Trying to allocate 129 38 -- Trying to allocate 129 19 -- Trying to allocate 129 37 -- Trying to allocate 129 28 -- Trying to allocate 129 37 Just for completness the base kernel without oom detection rework looks as follows: Trying to allocate 127 30 -- Trying to allocate 129 12 -- Trying to allocate 129 52 -- Trying to allocate 128 32 -- Trying to allocate 129 12 -- Trying to allocate 129 10 -- Trying to allocate 129 32 -- Trying to allocate 128 14 -- Trying to allocate 128 16 -- Trying to allocate 129 8 As we can see the success rate is much more volatile and smaller without this patch. So the patch not only makes the retry logic for costly requests more sensible the success rate is even higher. Signed-off-by:Michal Hocko <mhocko@suse.com> Acked-by:
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