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SubjectRe: [RESEND PATCH 1/2 -mm] mm: account lazy free pages separately
On 8/9/19 8:26 PM, Yang Shi wrote:
> Here the new counter is introduced for patch 2/2 to account deferred
> split THPs into available memory since NR_ANON_THPS may contain
> non-deferred split THPs.
> I could use an internal counter for deferred split THPs, but if it is
> accounted by mod_node_page_state, why not just show it in /proc/meminfo?

The answer to "Why not" is that it becomes part of userspace API (btw this
patchset should have CC'd linux-api@ - please do for further iterations) and
even if the implementation detail of deferred splitting might change in the
future, we'll basically have to keep the counter (even with 0 value) in
/proc/meminfo forever.

Also, quite recently we have added the following counter:

KReclaimable: Kernel allocations that the kernel will attempt to reclaim
under memory pressure. Includes SReclaimable (below), and other
direct allocations with a shrinker.

Although THP allocations are not exactly "kernel allocations", once they are
unmapped, they are in fact kernel-only, so IMHO it wouldn't be a big stretch to
add the lazy THP pages there?

> Or we fix NR_ANON_THPS and show deferred split THPs in /proc/meminfo?

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