From: "chenjun (AM)" <chenjun102@huawei.com>
To: Mike Rapoport <rppt@kernel.org>, Vlastimil Babka <vbabka@suse.cz>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"cl@linux.com" <cl@linux.com>,
"penberg@kernel.org" <penberg@kernel.org>,
"rientjes@google.com" <rientjes@google.com>,
"iamjoonsoo.kim@lge.com" <iamjoonsoo.kim@lge.com>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
Hyeonggon Yoo <42.hyeyoo@gmail.com>,
"xuqiang (M)" <xuqiang36@huawei.com>,
"Wangkefeng (OS Kernel Lab)" <wangkefeng.wang@huawei.com>,
Michal Hocko <mhocko@kernel.org>,
Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [PATCH] mm/slub: Reduce memory consumption in extreme scenarios
Date: Tue, 21 Mar 2023 09:30:23 +0000 [thread overview]
Message-ID: <c3a2280eff5c419ea14b6cad34474e08@huawei.com> (raw)
In-Reply-To: ZBgjZn7WOqO5ruws@kernel.org
在 2023/3/20 17:12, Mike Rapoport 写道:
> 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?
>
#define gfp_no_reclaim(gfpflag) (gfpflag & ~__GFP_DIRECT_RECLAIM)
And here,
pc.flags = gfp_no_reclaim(gfpflags) | __GFP_THISNODE.
Do I get it right?
next prev parent reply other threads:[~2023-03-21 9:30 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-14 12:34 [PATCH] mm/slub: Reduce memory consumption in extreme scenarios Chen Jun
2023-03-14 14:41 ` Vlastimil Babka
2023-03-17 11:32 ` chenjun (AM)
2023-03-17 12:06 ` Vlastimil Babka
2023-03-19 7:22 ` chenjun (AM)
2023-03-20 8:05 ` Vlastimil Babka
2023-03-20 9:12 ` Mike Rapoport
2023-03-21 9:30 ` chenjun (AM) [this message]
2023-03-29 8:41 ` Vlastimil Babka
2023-03-21 9:41 ` Vlastimil Babka
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