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

[David Hildenbrand]

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
> > path.
>
> 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.

--
Cheers,

David / dhildenb