linux-kernel - Re: [PATCH v4 01/25] mm: Introduce struct folio

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Date:   Mon, 22 Mar 2021 12:52:40 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Balbir Singh <bsingharora@...il.com>,
        Matthew Wilcox <willy@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v4 01/25] mm: Introduce struct folio

Excerpts from Matthew Wilcox's message of March 19, 2021 11:25 am:
> On Fri, Mar 19, 2021 at 10:56:45AM +1100, Balbir Singh wrote:
>> On Fri, Mar 05, 2021 at 04:18:37AM +0000, Matthew Wilcox (Oracle) wrote:
>> > A struct folio refers to an entire (possibly compound) page.  A function
>> > which takes a struct folio argument declares that it will operate on the
>> > entire compound page, not just PAGE_SIZE bytes.  In return, the caller
>> > guarantees that the pointer it is passing does not point to a tail page.
>> >
>> 
>> Is this a part of a larger use case or general cleanup/refactor where
>> the split between page and folio simplify programming?
> 
> The goal here is to manage memory in larger chunks.  Pages are now too
> small for just about every workload.  Even compiling the kernel sees a 7%
> performance improvement just by doing readahead using relatively small
> THPs (16k-256k).  You can see that work here:
> https://git.infradead.org/users/willy/pagecache.git/shortlog/refs/heads/master

The 7% improvement comes from cache cold kbuild by improving IO
patterns?

Just wondering what kind of readahead is enabled by this that can't
be done with base page size.

Thanks,
Nick