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    SubjectRe: [PATCH] mm, compaction: move high_pfn to the for loop scope.
    On Mon, Jan 18, 2021 at 03:41:26PM +0800, Rokudo Yan wrote:
    > In fast_isolate_freepages, high_pfn will be used if a prefered one(PFN >= low_fn) not found. But the high_pfn
    > is not reset before searching an free area, so when it was used as freepage, it may from another free area searched before.
    > And move_freelist_head(freelist, freepage) will have unexpected behavior(eg. corrupt the MOVABLE freelist)
    >
    > Unable to handle kernel paging request at virtual address dead000000000200
    > Mem abort info:
    > ESR = 0x96000044
    > Exception class = DABT (current EL), IL = 32 bits
    > SET = 0, FnV = 0
    > EA = 0, S1PTW = 0
    > Data abort info:
    > ISV = 0, ISS = 0x00000044
    > CM = 0, WnR = 1
    > [dead000000000200] address between user and kernel address ranges
    >
    > -000|list_cut_before(inline)
    > -000|move_freelist_head(inline)
    > -000|fast_isolate_freepages(inline)
    > -000|isolate_freepages(inline)
    > -000|compaction_alloc(?, ?)
    > -001|unmap_and_move(inline)
    > -001|migrate_pages([NSD:0xFFFFFF80088CBBD0] from = 0xFFFFFF80088CBD88, [NSD:0xFFFFFF80088CBBC8] get_new_p
    > -002|__read_once_size(inline)
    > -002|static_key_count(inline)
    > -002|static_key_false(inline)
    > -002|trace_mm_compaction_migratepages(inline)
    > -002|compact_zone(?, [NSD:0xFFFFFF80088CBCB0] capc = 0x0)
    > -003|kcompactd_do_work(inline)
    > -003|kcompactd([X19] p = 0xFFFFFF93227FBC40)
    > -004|kthread([X20] _create = 0xFFFFFFE1AFB26380)
    > -005|ret_from_fork(asm)
    > ---|end of frame
    >
    > The issue was reported on an smart phone product with 6GB ram and 3GB zram as swap device.
    >
    > This patch fixes the issue by reset high_pfn before searching each free area, which ensure
    > freepage and freelist match when call move_freelist_head in fast_isolate_freepages().
    >
    > Fixes: 5a811889de10f1eb ("mm, compaction: use free lists to quickly locate a migration target")
    >
    > Signed-off-by: Rokudo Yan <wu-yan@tcl.com>

    Other than a fixes line, I do not think this changed so my previous Ack
    still applies

    Acked-by: Mel Gorman <mgorman@techsingularity.net>

    --
    Mel Gorman
    SUSE Labs

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