linux-kernel - Re: [PATCH 2/2] mm, thp: consolidate THP gfp handling into alloc_hugepage_direct

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Message-ID: <20181025161410.GT18839@dhcp22.suse.cz>
Date:   Thu, 25 Oct 2018 18:14:10 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Mel Gorman <mgorman@...e.de>,
        David Rientjes <rientjes@...gle.com>,
        Andrea Argangeli <andrea@...nel.org>,
        Zi Yan <zi.yan@...rutgers.edu>,
        Stefan Priebe - Profihost AG <s.priebe@...fihost.ag>,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm, thp: consolidate THP gfp handling into
 alloc_hugepage_direct_gfpmask

On Thu 25-10-18 06:56:37, Vlastimil Babka wrote:
> On 10/25/18 1:17 AM, Andrew Morton wrote:
> > On Mon, 22 Oct 2018 15:27:54 +0200 Vlastimil Babka <vbabka@...e.cz> wrote:
> > 
> >>> : Moreover the oriinal code allowed to trigger
> >>> : 	WARN_ON_ONCE(policy->mode == MPOL_BIND && (gfp & __GFP_THISNODE));
> >>> : in policy_node if the requested node (e.g. cpu local one) was outside of
> >>> : the mbind nodemask. This is not possible now. We haven't heard about any
> >>> : such warning yet so it is unlikely that it happens but still a signal of
> >>> : a wrong code layering.
> >>
> >> Ah, as I said in the other mail, I think it's inaccurate, the warning
> >> was not possible to hit.
> >>
> >> There's also a slight difference wrt MPOL_BIND. The previous code would
> >> avoid using __GFP_THISNODE if the local node was outside of
> >> policy_nodemask(). After your patch __GFP_THISNODE is avoided for all
> >> MPOL_BIND policies. So there's a difference that if local node is
> >> actually allowed by the bind policy's nodemask, previously
> >> __GFP_THISNODE would be added, but now it won't be. I don't think it
> >> matters that much though, but maybe the changelog could say that
> >> (instead of the inaccurate note about warning). Note the other policy
> >> where nodemask is relevant is MPOL_INTERLEAVE, and that's unchanged by
> >> this patch.
> > 
> > So the above could go into the changelog, yes?
> 
> Yeah.

Andrew. Do you want me to repost the patch or you plan to update the
changelog yourself?
-- 
Michal Hocko
SUSE Labs