linux-kernel - RE: [PATCH] mm, compaction: fix fast_isolate

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Date:   Fri, 9 Dec 2022 09:19:37 +0000
From:   "Akira Naribayashi (Fujitsu)" <a.naribayashi@...itsu.com>
To:     'Mel Gorman' <mgorman@...hsingularity.net>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "rientjes@...gle.com" <rientjes@...gle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "Akira Naribayashi (Fujitsu)" <a.naribayashi@...itsu.com>
Subject: RE: [PATCH] mm, compaction: fix fast_isolate_around() to stay within
 boundaries

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