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

[Matthew Wilcox <willy@infradead.org>]

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 ;-)