linux-kernel - Re: [RFC PATCH 3/3] hugetlbfs: don't retry when pool page allocations start to fail

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Date:   Wed, 31 Jul 2019 15:23:51 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mike Kravetz <mike.kravetz@...cle.com>,
        Mel Gorman <mgorman@...e.de>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Hillf Danton <hdanton@...a.com>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 3/3] hugetlbfs: don't retry when pool page allocations
 start to fail

On 7/25/19 7:15 PM, Mike Kravetz wrote:
> On 7/25/19 1:13 AM, Mel Gorman wrote:
>> On Wed, Jul 24, 2019 at 10:50:14AM -0700, Mike Kravetz wrote:
>>> When allocating hugetlbfs pool pages via /proc/sys/vm/nr_hugepages,
>>> the pages will be interleaved between all nodes of the system.  If
>>> nodes are not equal, it is quite possible for one node to fill up
>>> before the others.  When this happens, the code still attempts to
>>> allocate pages from the full node.  This results in calls to direct
>>> reclaim and compaction which slow things down considerably.
>>>
>>> When allocating pool pages, note the state of the previous allocation
>>> for each node.  If previous allocation failed, do not use the
>>> aggressive retry algorithm on successive attempts.  The allocation
>>> will still succeed if there is memory available, but it will not try
>>> as hard to free up memory.
>>>
>>> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
>>
>> set_max_huge_pages can fail the NODEMASK_ALLOC() alloc which you handle
>> *but* in the event of an allocation failure this bug can silently recur.
>> An informational message might be justified in that case in case the
>> stall should recur with no hint as to why.
> 
> Right.
> Perhaps a NODEMASK_ALLOC() failure should just result in a quick exit/error.
> If we can't allocate a node mask, it is unlikely we will be able to allocate
> a/any huge pages.  And, the system must be extremely low on memory and there
> are likely other bigger issues.

Agreed. But I would perhaps drop __GFP_NORETRY from the mask allocation
as that can fail for transient conditions.

> There have been discussions elsewhere about discontinuing the use of
> NODEMASK_ALLOC() and just putting the mask on the stack.  That may be
> acceptable here as well.
> 
>>                                            Technically passing NULL into
>> NODEMASK_FREE is also safe as kfree (if used for that kernel config) can
>> handle freeing of a NULL pointer. However, that is cosmetic more than
>> anything. Whether you decide to change either or not;
> 
> Yes.
> I will clean up with an updated series after more feedback.
> 
>>
>> Acked-by: Mel Gorman <mgorman@...e.de>
>>
> 
> Thanks!
>