Re: [PATCH] mm: net: memcg accounting for TCP rx zerocopy

On Tue, Jan 19, 2021 at 07:31:51PM -0800, Arjun Roy wrote:

On Wed, Jan 13, 2021 at 11:55 AM Shakeel Butt [off-list ref] wrote:

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On Wed, Jan 13, 2021 at 11:49 AM Yang Shi [off-list ref] wrote:

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On Wed, Jan 13, 2021 at 11:13 AM Shakeel Butt [off-list ref] wrote:

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On Wed, Jan 13, 2021 at 10:43 AM Roman Gushchin [off-list ref] wrote:

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On Tue, Jan 12, 2021 at 04:18:44PM -0800, Shakeel Butt wrote:

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On Tue, Jan 12, 2021 at 4:12 PM Arjun Roy [off-list ref] wrote:

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On Tue, Jan 12, 2021 at 3:48 PM Roman Gushchin [off-list ref] wrote:

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Historically we have a corresponding vmstat counter to each charged page.
It helps with finding accounting/stastistics issues: we can check that
memory.current ~= anon + file + sock + slab + percpu + stack.
It would be nice to preserve such ability.

Perhaps one option would be to have it count as a file page, or have a
new category.

Oh these are actually already accounted for in NR_FILE_MAPPED.

Well, it's confusing. Can't we fix this by looking at the new page memcg flag?

Yes we can. I am inclined more towards just using NR_FILE_PAGES (as
Arjun suggested) instead of adding a new metric.

IMHO I tend to agree with Roman, it sounds confusing. I'm not sure how
people relies on the counter to have ballpark estimation about the
amount of reclaimable memory for specific memcg, but they are
unreclaimable. And, I don't think they are accounted to
NR_ACTIVE_FILE/NR_INACTIVE_FILE, right? So, the disparity between
NR_FILE_PAGES and NR_{IN}ACTIVE_FILE may be confusing either.

Please note that due to shmem/tmpfs there is already disparity between
NR_FILE_PAGES and NR_{IN}ACTIVE_FILE.

BTW I don't have a strong opinion against adding a new metric. If
there is consensus we can add one.

Just wanted to see if there were any thoughts/consensus on what the
best way to proceed is - should there be a v2 patch with specific
changes? Or is NR_FILE_PAGES alright?

I struggle to see why these pages should be considered file pages.
(NR_FILE_MAPPED is a different story).
I'm ok with slab/kmem, sock and a new metric, we can discuss what's
the best option out of three.

And similar query, for pre-charging vs. post charging.

IMO double accounting is bad. If it means post charging, I vote for
post charging.

Thanks!