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Date:   Mon, 28 Jun 2021 10:48:05 -0400
From:   Dave Jones <davej@codemonkey.org.uk>
To:     Mel Gorman <mgorman@techsingularity.net>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] mm/page_alloc: do bulk array bounds check after checking
 populated elements
Message-ID: <20210628144805.GA3687@codemonkey.org.uk>
Mail-Followup-To: Dave Jones <davej@codemonkey.org.uk>,
        Mel Gorman <mgorman@techsingularity.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Vlastimil Babka <vbabka@suse.cz>, Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
References: <20210618125102.GU30378@techsingularity.net>
 <20210628042759.GA19686@codemonkey.org.uk>
 <20210628115322.GA3840@techsingularity.net>
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On Mon, Jun 28, 2021 at 12:53:23PM +0100, Mel Gorman wrote:

 > > This made it into 5.13 final, and completely breaks NFSD for me (Serving tcp v3 mounts).
 > > Existing mounts on clients hang, as do new mounts from new clients.
 > > Rebooting the server back to rc7 everything recovers.  Bisect lands on
 > > this commit.
 > 
 > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
 > index ef2265f86b91..04220581579c 100644
 > --- a/mm/page_alloc.c
 > +++ b/mm/page_alloc.c
 > @@ -5058,7 +5058,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
 >  
 >  	/* Already populated array? */
 >  	if (unlikely(page_array && nr_pages - nr_populated == 0))
 > -		return 0;
 > +		return nr_populated;

Yep, this works.

	Dave