linux-kernel - Re: [PATCH RFC v2 00/10] SLUB percpu sheaves

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Message-ID: <CAJuCfpFVopL+sMdU4bLRxs+HS_WPCmFZBdCmwE8qV2Dpa5WZnA@mail.gmail.com>
Date: Fri, 14 Mar 2025 10:10:23 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Suren Baghdasaryan <surenb@...gle.com>, Kent Overstreet <kent.overstreet@...ux.dev>, 
	Christoph Lameter <cl@...ux.com>, David Rientjes <rientjes@...gle.com>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Hyeonggon Yoo <42.hyeyoo@...il.com>, 
	Uladzislau Rezki <urezki@...il.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	rcu@...r.kernel.org, maple-tree@...ts.infradead.org, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Alexei Starovoitov <ast@...nel.org>, 
	Sidhartha Kumar <sidhartha.kumar@...cle.com>
Subject: Re: [PATCH RFC v2 00/10] SLUB percpu sheaves

On Tue, Mar 4, 2025 at 11:08 AM Liam R. Howlett <Liam.Howlett@...cle.com> wrote:
>
> * Vlastimil Babka <vbabka@...e.cz> [250304 05:55]:
> > On 2/25/25 21:26, Suren Baghdasaryan wrote:
> > > On Mon, Feb 24, 2025 at 1:12 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
> > >>
> > >> >
> > >> > > The values represent the total time it took to perform mmap syscalls, less is
> > >> > > better.
> > >> > >
> > >> > > (1)                  baseline       control
> > >> > > Little core       7.58327       6.614939 (-12.77%)
> > >> > > Medium core  2.125315     1.428702 (-32.78%)
> > >> > > Big core          0.514673     0.422948 (-17.82%)
> > >> > >
> > >> > > (2)                  baseline      control
> > >> > > Little core       7.58327       5.141478 (-32.20%)
> > >> > > Medium core  2.125315     0.427692 (-79.88%)
> > >> > > Big core          0.514673    0.046642 (-90.94%)
> > >> > >
> > >> > > (3)                   baseline      control
> > >> > > Little core        7.58327      4.779624 (-36.97%)
> > >> > > Medium core   2.125315    0.450368 (-78.81%)
> > >> > > Big core           0.514673    0.037776 (-92.66%)
> > >
> > > (4)                   baseline      control
> > > Little core        7.58327      4.642977 (-38.77%)
> > > Medium core   2.125315    0.373692 (-82.42%)
> > > Big core           0.514673    0.043613 (-91.53%)
> > >
> > > I think the difference between (3) and (4) is noise.
> > > Thanks,
> > > Suren.
> >
> > Hi, as we discussed yesterday, it would be useful to set the baseline to
> > include everything before sheaves as that's already on the way to 6.15, so
> > we can see more clearly what sheaves do relative to that. So at this point
> > it's the vma lock conversion including TYPESAFE_BY_RCU (that's not undone,
> > thus like in scenario (4)), and benchmark the following:
> >
> > - baseline - vma locking conversion with TYPESAFE_BY_RCU
> > - baseline+maple tree node reduction from mm-unstable (Liam might point out
> > which patches?)
>
> Sid's patches [1] are already in mm-unstable.
>
>
> > - the above + this series + sheaves enabled for vm_area_struct cache
> > - the above + full maple node sheaves conversion [1]
> > - the above + the top-most patches from [1] that are optimizations with a
> > tradeoff (not clear win-win) so it would be good to know if they are useful
> >
> > [1] currently the 4 commits here:
> > https://web.git.kernel.org/pub/scm/linux/kernel/git/vbabka/linux.git/log/?h=slub-percpu-sheaves-v2-maple
> > from "maple_tree: Sheaf conversion" to "maple_tree: Clean up sheaf"
> > but as Liam noted, they won't cherry pick without conflict once maple tree
> > node reduction is backported, but he's working on a rebase
>
> Rebased maple tree sheaves, patches are here [2].

Hi Folks,
Sorry for the delay. I got the numbers last week but they looked a bit
weird, so I reran the test increasing the number of iterations to make
sure noise is not a factor. That took most of this week. Below are the
results. Please note that I had to backport the patchsets to 6.12
because that's the closest stable Android kernel I can use. I measure
cumulative time to execute mmap syscalls, so the smaller the number
the better mmap performance is:

baseline: 6.12 + vm_lock conversion and TYPESAFE_BY_RCU
config1: baseline + Sid's patches [1]
config2: sheaves RFC
config3: config1 + vm_area_struct with sheaves
config4: config2 + maple_tree Sheaf conversion [2]
config5: config3 + 2 last optimization patches from [3]

               config1     config2     config3     config4     config5
Little core    -0.10%      -10.10%     -12.89%     -10.02%     -13.64%
Mid core       -21.05%     -37.31%     -44.97%     -15.81%     -22.15%
Big core       -17.17%     -34.41%     -45.68%     -11.39%     -15.29%

[1] https://lore.kernel.org/linux-mm/20250227204823.758784-1-sidhartha.kumar@oracle.com/
[2] https://www.infradead.org/git/?p=users/jedix/linux-maple.git;a=shortlog;h=refs/heads/sheaves_rebase_20250304
[3] https://web.git.kernel.org/pub/scm/linux/kernel/git/vbabka/linux.git/log/?h=slub-percpu-sheaves-v2-maple

>From the numbers, it looks like config4 regresses the performance and
that's what looked weird to me last week and I wanted to confirm this.
But from sheaves POV, it looks like they provide the benefits I saw
before. Sid's patches which I did not test separately before also look
beneficial.
Thanks,
Suren.

>
>
> >
> >
> ...
>
> Thanks,
> Liam
>
> [1]. https://lore.kernel.org/linux-mm/20250227204823.758784-1-sidhartha.kumar@oracle.com/
> [2]. https://www.infradead.org/git/?p=users/jedix/linux-maple.git;a=shortlog;h=refs/heads/sheaves_rebase_20250304