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    SubjectRE: [PATCH] mm, compaction: fix fast_isolate_around() to stay within boundaries
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    On Wed, 23 Nov 2022 10:26:05 +0000, Mei Gorman wrote:
    > On Wed, Nov 09, 2022 at 05:41:12AM +0000, Akira Naribayashi (Fujitsu) wrote:
    > > On Mon, 7 Nov 2022 15:43:56 +0000, Mei Gorman wrote:
    > > > On Mon, Nov 07, 2022 at 12:32:34PM +0000, Akira Naribayashi (Fujitsu) wrote:
    > > > > > Under what circumstances will this panic occur? I assume those
    > > > > > circumstnces are pretty rare, give that 6e2b7044c1992 was nearly two
    > > > > > years ago.
    > > > > >
    > > > > > Did you consider the desirability of backporting this fix into earlier
    > > > > > kernels?
    > > > >
    > > > >
    > > > > Panic can occur on systems with multiple zones in a single pageblock.
    > > > >
    > > >
    > > > Please provide an example of the panic and the zoneinfo.
    > >
    > > This issue is occurring in our customer's environment and cannot
    > > be shared publicly as it contains customer information.
    > > Also, the panic is occurring with the kernel in RHEL and may not
    > > panic with Upstream's community kernel.
    > > In other words, it is possible to panic on older kernels.
    > > I think this fix should be backported to stable kernel series.
    > >
    > > > > The reason it is rare is that it only happens in special configurations.
    > > >
    > > > How is this special configuration created?
    > >
    > > This is the case when the node boundary is not aligned to pageblock boundary.
    >
    > In that case, does this work to avoid rescanning an area that was already
    > isolated?

    In the case of your patch, I think I need to clamp the isolated_end as well.
    Because sometimes isolated_end < start_pfn(value before entering Scan after) < end_pfn.

    After re-reading the source, I think the problem is that min_pfn and low_pfn
    can be out of range in fast_isolate_freepages.
    How about the following patch?

    diff --git a/mm/compaction.c b/mm/compaction.c
    index 1f6da31dd9a5..b67b82bb4944 100644
    --- a/mm/compaction.c
    +++ b/mm/compaction.c
    @@ -1436,6 +1436,11 @@ fast_isolate_freepages(struct compact_control *cc)
    if (WARN_ON_ONCE(min_pfn > low_pfn))
    low_pfn = min_pfn;

    + if (min_pfn < cc->migrate_pfn)
    + min_pfn = cc->migrate_pfn;
    + if (low_pfn < cc->migrate_pfn)
    + low_pfn = cc->migrate_pfn;
    +
    /*
    * Search starts from the last successful isolation order or the next
    * order to search after a previous failure
    \
     
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