[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ZBgjZn7WOqO5ruws@kernel.org>
Date: Mon, 20 Mar 2023 11:12:06 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: "chenjun (AM)" <chenjun102@...wei.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"cl@...ux.com" <cl@...ux.com>,
"penberg@...nel.org" <penberg@...nel.org>,
"rientjes@...gle.com" <rientjes@...gle.com>,
"iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
Hyeonggon Yoo <42.hyeyoo@...il.com>,
"xuqiang (M)" <xuqiang36@...wei.com>,
"Wangkefeng (OS Kernel Lab)" <wangkefeng.wang@...wei.com>,
Michal Hocko <mhocko@...nel.org>,
Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH] mm/slub: Reduce memory consumption in extreme scenarios
On Mon, Mar 20, 2023 at 09:05:57AM +0100, Vlastimil Babka wrote:
> On 3/19/23 08:22, chenjun (AM) wrote:
> > 在 2023/3/17 20:06, Vlastimil Babka 写道:
> >> On 3/17/23 12:32, chenjun (AM) wrote:
> >>> 在 2023/3/14 22:41, Vlastimil Babka 写道:
> >>>>> pc.flags = gfpflags;
> >>>>> +
> >>>>> + /*
> >>>>> + * when (node != NUMA_NO_NODE) && (gfpflags & __GFP_THISNODE)
> >>>>> + * 1) try to get a partial slab from target node with __GFP_THISNODE.
> >>>>> + * 2) if 1) failed, try to allocate a new slab from target node with
> >>>>> + * __GFP_THISNODE.
> >>>>> + * 3) if 2) failed, retry 1) and 2) without __GFP_THISNODE constraint.
> >>>>> + */
> >>>>> + if (node != NUMA_NO_NODE && !(gfpflags & __GFP_THISNODE) && try_thisnode)
> >>>>> + pc.flags |= __GFP_THISNODE;
> >>>>
> >>>> Hmm I'm thinking we should also perhaps remove direct reclaim possibilities
> >>>> from the attempt 2). In your qemu test it should make no difference, as it
> >>>> fills everything with kernel memory that is not reclaimable. But in practice
> >>>> the target node might be filled with user memory, and I think it's better to
> >>>> quickly allocate on a different node than spend time in direct reclaim. So
> >>>> the following should work I think?
> >>>>
> >>>> pc.flags = GFP_NOWAIT | __GFP_NOWARN |__GFP_THISNODE
> >>>>
> >>>
> >>> Hmm, Should it be that:
> >>>
> >>> pc.flags |= GFP_NOWAIT | __GFP_NOWARN |__GFP_THISNODE
> >>
> >> No, we need to ignore the other reclaim-related flags that the caller
> >> passed, or it wouldn't work as intended.
> >> The danger is that we ignore some flag that would be necessary to pass, but
> >> I don't think there's any?
> >>
> >>
> >
> > If we ignore __GFP_ZERO passed by kzalloc, kzalloc will not work.
> > Could we just unmask __GFP_RECLAIMABLE | __GFP_RECLAIM?
> >
> > pc.flags &= ~(__GFP_RECLAIMABLE | __GFP_RECLAIM)
> > pc.flags |= __GFP_THISNODE
>
> __GFP_RECLAIMABLE would be wrong, but also ignored as new_slab() does:
> flags & (GFP_RECLAIM_MASK | GFP_CONSTRAINT_MASK)
>
> which would filter out __GFP_ZERO as well. That's not a problem as kzalloc()
> will zero out the individual allocated objects, so it doesn't matter if we
> don't zero out the whole slab page.
>
> But I wonder, if we're not past due time for a helper e.g.
> gfp_opportunistic(flags) that would turn any allocation flags to a
> GFP_NOWAIT while keeping the rest of relevant flags intact, and thus there
> would be one canonical way to do it - I'm sure there's a number of places
> with their own variants now?
> With such helper we'd just add __GFP_THISNODE to the result here as that's
> specific to this particular opportunistic allocation.
I like the idea, but maybe gfp_no_reclaim() would be clearer?
--
Sincerely yours,
Mike.
Powered by blists - more mailing lists