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Mon, 02 Dec 2024 12:36:31 -0800 (PST) MIME-Version: 1.0 References: <20241202184154.19321-1-ryncsn@gmail.com> <20241202184154.19321-5-ryncsn@gmail.com> In-Reply-To: From: Yosry Ahmed Date: Mon, 2 Dec 2024 12:35:55 -0800 Message-ID: Subject: Re: [PATCH 4/4] mm, swap_cgroup: remove global swap cgroup lock To: Kairui Song Cc: linux-mm@kvack.org, Andrew Morton , Chris Li , Hugh Dickins , "Huang, Ying" , Roman Gushchin , Shakeel Butt , Johannes Weiner , Barry Song , Michal Hocko , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 4ynu91ukadoq49on9frkeqwaiadarat9 X-Rspamd-Queue-Id: C9E0940016 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1733171778-337192 X-HE-Meta: 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 vM0xw/FX VinCUE8cbsY6aNTD0HBu3dGNiSEzlHSLELLxFGf6AjDPpP8keWezd+RvQmqfpmyKoYLjOBtEyoOyLIwbXWYq25BvYlpFaWMsrD8YDrqTO7nG5OgfrKwy0kT1fUyC++Hz26QExadGFndC6laMt8Mkz7/OAVHfvKjSbhM9s8lx6qHQ0PYgttnLC3C1JzqY+yglDJjgYNy22vRji1QW+LjxGJIsIxY4NDLT25LWs/C8VbJvKBwifuzdi3ebfMGhE/696AFKwphJggm3dJnxPal4qjfqA/S4k74y2zgQMiTEnFP6e/DN7CrDIunPaqg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Dec 2, 2024 at 11:28=E2=80=AFAM Yosry Ahmed = wrote: > > On Mon, Dec 2, 2024 at 10:42=E2=80=AFAM Kairui Song wr= ote: > > > > From: Kairui Song > > > > commit e9e58a4ec3b1 ("memcg: avoid use cmpxchg in swap cgroup maintaina= nce") > > replaced the cmpxchg/xchg with a global irq spinlock because some archs > > doesn't support 2 bytes cmpxchg/xchg. Clearly this won't scale well. > > > > And as commented in swap_cgroup.c, this lock is not needed for map > > synchronization. > > > > Emulation of 2 bytes cmpxchg/xchg with atomic isn't hard, so implement > > it to get rid of this lock. > > > > Testing using 64G brd and build with build kernel with make -j96 in 1.5= G > > memory cgroup using 4k folios showed below improvement (10 test run): > > > > Before this series: > > Sys time: 10730.08 (stdev 49.030728) > > Real time: 171.03 (stdev 0.850355) > > > > After this commit: > > Sys time: 9612.24 (stdev 66.310789), -10.42% > > Real time: 159.78 (stdev 0.577193), -6.57% > > > > With 64k folios and 2G memcg: > > Before this series: > > Sys time: 7626.77 (stdev 43.545517) > > Real time: 136.22 (stdev 1.265544) > > > > After this commit: > > Sys time: 6936.03 (stdev 39.996280), -9.06% > > Real time: 129.65 (stdev 0.880039), -4.82% > > > > Sequential swapout of 8G 4k zero folios (24 test run): > > Before this series: > > 5461409.12 us (stdev 183957.827084) > > > > After this commit: > > 5420447.26 us (stdev 196419.240317) > > > > Sequential swapin of 8G 4k zero folios (24 test run): > > Before this series: > > 19736958.916667 us (stdev 189027.246676) > > > > After this commit: > > 19662182.629630 us (stdev 172717.640614) > > > > Performance is better or at least not worse for all tests above. > > > > Signed-off-by: Kairui Song > > --- > > mm/swap_cgroup.c | 56 +++++++++++++++++++++++++++++++++++------------- > > 1 file changed, 41 insertions(+), 15 deletions(-) > > > > diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c > > index a76afdc3666a..028f5e6be3f0 100644 > > --- a/mm/swap_cgroup.c > > +++ b/mm/swap_cgroup.c > > @@ -5,6 +5,15 @@ > > > > #include /* depends on mm.h include */ > > > > +#define ID_PER_UNIT (sizeof(atomic_t) / sizeof(unsigned short)) > > +struct swap_cgroup_unit { > > + union { > > + int raw; > > + atomic_t val; > > + unsigned short __id[ID_PER_UNIT]; > > + }; > > +}; > > This doubles the size of the per-entry data, right? Oh we don't, we just store 2 ids in an int instead of storing each id individually. But the question below still stands, can't we just use cmpxchg() directly on the id? > > Why do we need this? I thought cmpxchg() supports multiple sizes and > will already do the emulation for us.