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    SubjectRe: [PATCH RESEND 0/8] hugetlb: add demote/split page functionality
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    On 8/30/21 3:11 AM, Vlastimil Babka wrote:
    > On 8/28/21 01:04, Mike Kravetz wrote:
    >> On 8/27/21 10:22 AM, Vlastimil Babka wrote:
    >> I 'may' have been over stressing the system with all CPUs doing file
    >> reads to fill the page cache with clean pages. I certainly need to
    >> spend some more debug/analysis time on this.
    >
    > Hm that *could* play a role, as these will allow reclaim to make progress, but
    > also the reclaimed pages might be stolen immediately and compaction will return
    > COMPACT_SKIPPED and in should_compact_retry() we might go through this code path:
    >
    > /*
    > * compaction was skipped because there are not enough order-0 pages
    > * to work with, so we retry only if it looks like reclaim can help.
    > */
    > if (compaction_needs_reclaim(compact_result)) {
    > ret = compaction_zonelist_suitable(ac, order, alloc_flags);
    > goto out;
    > }
    >
    > where compaction_zonelist_suitable() will return true because it appears
    > reclaim can free pages to allow progress. And there are no max retries
    > applied for this case.
    > With the reclaim and compaction tracepoints it should be possible to
    > confirm this scenario.

    Here is some very high level information from a long stall that was
    interrupted. This was an order 9 allocation from alloc_buddy_huge_page().

    55269.530564] __alloc_pages_slowpath: jiffies 47329325 tries 609673 cpu_tries 1 node 0 FAIL
    [55269.539893] r_tries 25 c_tries 609647 reclaim 47325161 compact 607

    Yes, in __alloc_pages_slowpath for 47329325 jiffies before being interrupted.
    should_reclaim_retry returned true 25 times and should_compact_retry returned
    true 609647 times.
    Almost all time (47325161 jiffies) spent in __alloc_pages_direct_reclaim, and
    607 jiffies spent in __alloc_pages_direct_compact.

    Looks like both
    reclaim retries > MAX_RECLAIM_RETRIES
    and
    compaction retries > MAX_COMPACT_RETRIES
    --
    Mike Kravetz

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