linux-kernel - Re: [PATCH 1/3] mm: introduce NR_INDIRECTLY_RECLAIMABLE

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Date:   Wed, 25 Apr 2018 17:47:26 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Roman Gushchin <guro@...com>,
        Vijayanand Jitta <vjitta@...eaurora.org>
Cc:     vinayak menon <vinayakm.list@...il.com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH 1/3] mm: introduce NR_INDIRECTLY_RECLAIMABLE_BYTES

On 04/25/2018 02:52 PM, Roman Gushchin wrote:
> On Wed, Apr 25, 2018 at 09:19:29AM +0530, Vijayanand Jitta wrote:
>>>>>> Idk, I don't like the idea of adding a counter outside of the vm counters
>>>>>> infrastructure, and I definitely wouldn't touch the exposed
>>>>>> nr_slab_reclaimable and nr_slab_unreclaimable fields.
>>>>>
>>>>> We would be just making the reported values more precise wrt reality.
>>>>
>>>> It depends on if we believe that only slab memory can be reclaimable
>>>> or not. If yes, this is true, otherwise not.
>>>>
>>>> My guess is that some drivers (e.g. networking) might have buffers,
>>>> which are reclaimable under mempressure, and are allocated using
>>>> the page allocator. But I have to look closer...
>>>>
>>>
>>> One such case I have encountered is that of the ION page pool. The page pool
>>> registers a shrinker. When not in any memory pressure page pool can go high
>>> and thus cause an mmap to fail when OVERCOMMIT_GUESS is set. I can send
>>> a patch to account ION page pool pages in NR_INDIRECTLY_RECLAIMABLE_BYTES.

FYI, we have discussed this at LSF/MM and agreed to try the kmalloc
reclaimable caches idea. The existing counter could then remain for page
allocator users such as ION. It's a bit weird to have it in bytes and
not pages then, IMHO. What if we hid it from /proc/vmstat now so it
doesn't become ABI, and later convert it to page granularity and expose
it under a name such as "nr_other_reclaimable" ?

Vlastimil

> Perfect!
> This is exactly what I've expected.
> 
>>>
>>> Thanks,
>>> Vinayak
>>>
>>
>> As Vinayak mentioned NR_INDIRECTLY_RECLAIMABLE_BYTES can be used to solve the issue
>> with ION page pool when OVERCOMMIT_GUESS is set, the patch for the same can be 
>> found here https://lkml.org/lkml/2018/4/24/1288
> 
> This makes perfect sense to me.
> 
> Please, fell free to add:
> Acked-by: Roman Gushchin <guro@...com>
> 
> Thank you!
>