linux-kernel - Re: [RFC PATCH 0/1] Large folios in block buffered IO path

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Message-ID: <CAGudoHGnNDOQtmNXTG4dphNnQW1MD7idAa0fmvk8fBPF34sUCw@mail.gmail.com>
Date: Fri, 29 Nov 2024 00:31:24 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: Bharata B Rao <bharata@....com>
Cc: Matthew Wilcox <willy@...radead.org>, linux-block@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-mm@...ck.org, nikunj@....com, vbabka@...e.cz, david@...hat.com, 
	akpm@...ux-foundation.org, yuzhao@...gle.com, axboe@...nel.dk, 
	viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz, joshdon@...gle.com, 
	clm@...a.com
Subject: Re: [RFC PATCH 0/1] Large folios in block buffered IO path

On Thu, Nov 28, 2024 at 12:24 PM Bharata B Rao <bharata@....com> wrote:
>
> On 28-Nov-24 10:07 AM, Bharata B Rao wrote:
> > On 28-Nov-24 9:52 AM, Matthew Wilcox wrote:
> >> On Thu, Nov 28, 2024 at 09:31:50AM +0530, Bharata B Rao wrote:
> >>> However a point of concern is that FIO bandwidth comes down drastically
> >>> after the change.
> >>>
> >>>         default                inode_lock-fix
> >>> rw=30%
> >>> Instance 1    r=55.7GiB/s,w=23.9GiB/s        r=9616MiB/s,w=4121MiB/s
> >>> Instance 2    r=38.5GiB/s,w=16.5GiB/s        r=8482MiB/s,w=3635MiB/s
> >>> Instance 3    r=37.5GiB/s,w=16.1GiB/s        r=8609MiB/s,w=3690MiB/s
> >>> Instance 4    r=37.4GiB/s,w=16.0GiB/s        r=8486MiB/s,w=3637MiB/s
> >>
> >> Something this dramatic usually only happens when you enable a debugging
> >> option.  Can you recheck that you're running both A and B with the same
> >> debugging options both compiled in, and enabled?
> >
> > It is the same kernel tree with and w/o Mateusz's inode_lock changes to
> > block/fops.c. I see the config remains same for both the builds.
> >
> > Let me get a run for both base and patched case w/o running perf lock
> > contention to check if that makes a difference.
>
> Without perf lock contention
>
>                  default                         inode_lock-fix
> rw=30%
> Instance 1      r=54.6GiB/s,w=23.4GiB/s         r=11.4GiB/s,w=4992MiB/s
> Instance 2      r=52.7GiB/s,w=22.6GiB/s         r=11.4GiB/s,w=4981MiB/s
> Instance 3      r=53.3GiB/s,w=22.8GiB/s         r=12.7GiB/s,w=5575MiB/s
> Instance 4      r=37.7GiB/s,w=16.2GiB/s         r=10.4GiB/s,w=4581MiB/s
>

per my other e-mail can you follow willy's suggestion and increase the hash?

best case scenario this takes care of it and then some heuristic can
be added how to autosize the thing.

If someone feels like microoptimizing I also note there is magic infra
to have the size hotpatchable into generated asm instead of it being
read (see dentry cache as an example user).

-- 
Mateusz Guzik <mjguzik gmail.com>