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    Subject[PATCH v4 2/4] mm: failfast mode with __GFP_NORETRY in alloc_contig_range
    Date
    Contiguous memory allocation can be stalled due to waiting
    on page writeback and/or page lock which causes unpredictable
    delay. It's a unavoidable cost for the requestor to get *big*
    contiguous memory but it's expensive for *small* contiguous
    memory(e.g., order-4) because caller could retry the request
    in different range where would have easy migratable pages
    without stalling.

    This patch introduce __GFP_NORETRY as compaction gfp_mask in
    alloc_contig_range so it will fail fast without blocking
    when it encounters pages needed waiting.

    Signed-off-by: Minchan Kim <minchan@kernel.org>
    ---
    mm/page_alloc.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index b031a5ae0bd5..1cdc3ee0b22e 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -8491,12 +8491,16 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
    unsigned int nr_reclaimed;
    unsigned long pfn = start;
    unsigned int tries = 0;
    + unsigned int max_tries = 5;
    int ret = 0;
    struct migration_target_control mtc = {
    .nid = zone_to_nid(cc->zone),
    .gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
    };

    + if (cc->alloc_contig && cc->mode == MIGRATE_ASYNC)
    + max_tries = 1;
    +
    migrate_prep();

    while (pfn < end || !list_empty(&cc->migratepages)) {
    @@ -8513,7 +8517,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
    break;
    }
    tries = 0;
    - } else if (++tries == 5) {
    + } else if (++tries == max_tries) {
    ret = ret < 0 ? ret : -EBUSY;
    break;
    }
    @@ -8564,7 +8568,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
    .nr_migratepages = 0,
    .order = -1,
    .zone = page_zone(pfn_to_page(start)),
    - .mode = MIGRATE_SYNC,
    + .mode = gfp_mask & __GFP_NORETRY ? MIGRATE_ASYNC : MIGRATE_SYNC,
    .ignore_skip_hint = true,
    .no_set_skip_hint = true,
    .gfp_mask = current_gfp_context(gfp_mask),
    --
    2.30.0.296.g2bfb1c46d8-goog
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