Re: [PATCH 0/6] shmem: high order folios support in write path

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On 15.09.23 17:40, Matthew Wilcox wrote:
On Fri, Sep 15, 2023 at 05:36:27PM +0200, David Hildenbrand wrote:
On 15.09.23 17:34, Matthew Wilcox wrote:
No, it can't.  This patchset triggers only on write, not on read or page
fault, and it's conservative, so it will only allocate folios which are
entirely covered by the write.  IOW this is memory we must allocate in
order to satisfy the write; we're just allocating it in larger chunks
when we can.

Oh, good! I was assuming you would eventually over-allocate on the write

We might!  But that would be a different patchset, and it would be
subject to its own discussion.

Something else I've been wondering about is possibly reallocating the
pages on a write.  This would apply to both normal files and shmem.
If you read in a file one byte at a time, then overwrite a big chunk of
it with a large single write, that seems like a good signal that maybe
we should manage that part of the file as a single large chunk instead
of individual pages.  Maybe.

Lots of things for people who are obsessed with performance to play
with ;-)

:) Absolutely. ... because if nobody will be consuming that written memory any time soon, it might also be the wrong place for a large/huge folio.


David / dhildenb

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