linux-kernel - Re: [PATCH v13 000/137] Memory folios

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Date:   Mon, 12 Jul 2021 06:46:05 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v13 000/137] Memory folios

On Mon, Jul 12, 2021 at 04:04:44AM +0100, Matthew Wilcox (Oracle) wrote:
> Managing memory in 4KiB pages is a serious overhead.  Many benchmarks
> benefit from a larger "page size".  As an example, an earlier iteration
> of this idea which used compound pages (and wasn't particularly tuned)
> got a 7% performance boost when compiling the kernel.
> 
> Using compound pages or THPs exposes a weakness of our type system.
> Functions are often unprepared for compound pages to be passed to them,
> and may only act on PAGE_SIZE chunks.  Even functions which are aware of
> compound pages may expect a head page, and do the wrong thing if passed
> a tail page.
> 
> We also waste a lot of instructions ensuring that we're not looking at
> a tail page.  Almost every call to PageFoo() contains one or more hidden
> calls to compound_head().  This also happens for get_page(), put_page()
> and many more functions.
> 
> This patch series uses a new type, the struct folio, to manage memory.
> It converts enough of the page cache, iomap and XFS to use folios instead
> of pages, and then adds support for multi-page folios.  It passes xfstests
> (running on XFS) with no regressions compared to v5.14-rc1.

This seems to miss a changelog vs the previous version.  It also
includes a lot of the follow ups.  I think reviewing a series gets
rather hard at more than 30-ish patches, so chunking it up a little
more would be useful.