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Message-ID: <ZQR7CyddIQQAs3yb@casper.infradead.org>
Date: Fri, 15 Sep 2023 16:40:59 +0100
From: Matthew Wilcox <willy@...radead.org>
To: David Hildenbrand <david@...hat.com>
Cc: Daniel Gomez <da.gomez@...sung.com>,
"minchan@...nel.org" <minchan@...nel.org>,
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Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH 0/6] shmem: high order folios support in write path
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 ;-)
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