linux-kernel - Re: [PATCH] mm/page_alloc: do bulk array bounds check after checking populated elements

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Date:   Mon, 28 Jun 2021 16:03:48 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Dave Jones <davej@...emonkey.org.uk>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] mm/page_alloc: do bulk array bounds check after checking
 populated elements

On Mon, Jun 28, 2021 at 10:48:05AM -0400, Dave Jones wrote:
> 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.
> 

Thanks Dave, it passed a dbench test over NFS locally as well so I sent
a proper version of the patch. Hopefully it'll be picked up relatively
quickly and appear in a 5.13.1 release.

-- 
Mel Gorman
SUSE Labs