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    SubjectRe: [f2fs-dev] [PATCH] f2fs: initialize page->private when using for our internal use
    On Mon, Jul 05, 2021 at 11:04:21AM -0700, Jaegeuk Kim wrote:
    > On 07/05, Matthew Wilcox wrote:
    > > I think freshly allocated pages have a page->private of 0. ie this
    > > code in mm/page_alloc.c:
    > >
    > > page = rmqueue(ac->preferred_zoneref->zone, zone, order,
    > > gfp_mask, alloc_flags, ac->migratetype);
    > > if (page) {
    > > prep_new_page(page, order, gfp_mask, alloc_flags);
    > >
    > > where prep_new_page() calls post_alloc_hook() which contains:
    > > set_page_private(page, 0);
    >
    > Hmm, I can see it in 4.14 and 5.10 kernel.
    >
    > The trace is on:
    >
    > 30875 [ 1065.118750] c3 87 f2fs_migrate_page+0x354/0x45c
    > 30876 [ 1065.123872] c3 87 move_to_new_page+0x70/0x30c
    > 30877 [ 1065.128813] c3 87 migrate_pages+0x3a0/0x964
    > 30878 [ 1065.133583] c3 87 compact_zone+0x608/0xb04
    > 30879 [ 1065.138257] c3 87 kcompactd+0x378/0x4ec
    > 30880 [ 1065.142664] c3 87 kthread+0x11c/0x12c
    > 30881 [ 1065.146897] c3 87 ret_from_fork+0x10/0x18
    >
    > It seems compaction_alloc() gets a free page which doesn't reset the fields?

    I'm not really familiar with the compaction code. Mel, I see a call
    to post_alloc_hook() in split_map_pages(). Are there other ways of
    getting the compaction code to allocate a page which don't go through
    split_map_pages()?

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