On 04/25/2018 02:52 PM, Roman Gushchin wrote:

On Wed, Apr 25, 2018 at 09:19:29AM +0530, Vijayanand Jitta wrote:

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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.

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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 <redacted>

Thank you!