linux-kernel - Re: [patch for-4.20] Revert "mm, thp: consolidate THP gfp handling into alloc_hugepage_direct

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Message-ID: <296d9813-1dfe-f27c-8d2c-6f140d8a5b0d@suse.cz>
Date:   Fri, 7 Dec 2018 15:41:49 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     David Rientjes <rientjes@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        mgorman@...hsingularity.net, mhocko@...nel.org,
        ying.huang@...el.com, s.priebe@...fihost.ag,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        alex.williamson@...hat.com, lkp@...org, kirill@...temov.name,
        Andrew Morton <akpm@...ux-foundation.org>,
        zi.yan@...rutgers.edu
Subject: Re: [patch for-4.20] Revert "mm, thp: consolidate THP gfp handling
 into alloc_hugepage_direct_gfpmask"

On 12/6/18 11:00 PM, David Rientjes wrote:
> This reverts commit 89c83fb539f95491be80cdd5158e6f0ce329e317.
> 
> There are a couple of issues with 89c83fb539f9 independent of its partial 
> revert in 2f0799a0ffc0 ("mm, thp: restore node-local hugepage 
> allocations"):
> 
> Firstly, the interaction between alloc_hugepage_direct_gfpmask() and 
> alloc_pages_vma() is racy wrt __GFP_THISNODE and MPOL_BIND.  
> alloc_hugepage_direct_gfpmask() makes sure not to set __GFP_THISNODE for 
> an MPOL_BIND policy but the policy used in alloc_pages_vma() may not be 
> the same for shared vma policies, triggering the WARN_ON_ONCE() in 
> policy_node().

AFAICS 2f0799a0ffc0 removed the policy check in
alloc_hugepage_direct_gfpmask() comlpetely, so it's not racy and the
warning will always trigger for a MPOL_BIND policy right now?