linux-kernel - Re: [PATCH 5/6] mm: honor PF_MEMALLOC

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Message-ID: <20201204085401.GB25569@dhcp22.suse.cz>
Date:   Fri, 4 Dec 2020 09:54:01 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Sasha Levin <sashal@...nel.org>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, mike.kravetz@...cle.com,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH 5/6] mm: honor PF_MEMALLOC_NOMOVABLE for all allocations

On Fri 04-12-20 09:43:13, Michal Hocko wrote:
> On Thu 03-12-20 10:15:41, Pavel Tatashin wrote:
[...]
> > Also, current_gfp_context() is used elsewhere, and in some
> > places removing __GFP_MOVABLE from gfp_mask means that we will need to
> > also change other things. For example [1], in try_to_free_pages() we
> > call current_gfp_context(gfp_mask) which can reduce the maximum zone
> > idx, yet we simply set it to: reclaim_idx = gfp_zone(gfp_mask), not to
> > the newly determined gfp_mask.
> 
> Yes and the direct reclaim should honor the movable zone restriction.
> Why should we reclaim ZONE_MOVABLE when the allocation cannot really
> allocate from it? Or have I misunderstood your concern?

Btw. if we have gfp mask properly filtered for the fast path then we can
remove the additional call to current_gfp_context from the direct
reclaim path. Something for a separate patch.
-- 
Michal Hocko
SUSE Labs