linux-kernel - RE: [PATCH v6 0/3] mm: ZSWAP swap-out of mTHP folios

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <SJ0PR11MB567817BD31202F651F181B76C96C2@SJ0PR11MB5678.namprd11.prod.outlook.com>
Date: Fri, 20 Sep 2024 02:30:39 +0000
From: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
To: Yosry Ahmed <yosryahmed@...gle.com>, Nhat Pham <nphamcs@...il.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, "hannes@...xchg.org"
	<hannes@...xchg.org>, "chengming.zhou@...ux.dev" <chengming.zhou@...ux.dev>,
	"usamaarif642@...il.com" <usamaarif642@...il.com>, "ryan.roberts@....com"
	<ryan.roberts@....com>, "Huang, Ying" <ying.huang@...el.com>,
	"21cnbao@...il.com" <21cnbao@...il.com>, "akpm@...ux-foundation.org"
	<akpm@...ux-foundation.org>, "Zou, Nanhai" <nanhai.zou@...el.com>, "Feghali,
 Wajdi K" <wajdi.k.feghali@...el.com>, "Gopal, Vinodh"
	<vinodh.gopal@...el.com>, "Sridhar, Kanchana P"
	<kanchana.p.sridhar@...el.com>
Subject: RE: [PATCH v6 0/3] mm: ZSWAP swap-out of mTHP folios


> -----Original Message-----
> From: Yosry Ahmed <yosryahmed@...gle.com>
> Sent: Thursday, August 29, 2024 5:14 PM
> To: Nhat Pham <nphamcs@...il.com>
> Cc: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>; linux-
> kernel@...r.kernel.org; linux-mm@...ck.org; hannes@...xchg.org;
> chengming.zhou@...ux.dev; usamaarif642@...il.com;
> ryan.roberts@....com; Huang, Ying <ying.huang@...el.com>;
> 21cnbao@...il.com; akpm@...ux-foundation.org; Zou, Nanhai
> <nanhai.zou@...el.com>; Feghali, Wajdi K <wajdi.k.feghali@...el.com>;
> Gopal, Vinodh <vinodh.gopal@...el.com>
> Subject: Re: [PATCH v6 0/3] mm: ZSWAP swap-out of mTHP folios
> 
> On Thu, Aug 29, 2024 at 5:06 PM Nhat Pham <nphamcs@...il.com> wrote:
> >
> > On Thu, Aug 29, 2024 at 4:55 PM Yosry Ahmed <yosryahmed@...gle.com>
> wrote:
> > >
> > > On Thu, Aug 29, 2024 at 4:45 PM Nhat Pham <nphamcs@...il.com>
> wrote:
> > > I think it's also the fact that the processes exit right after they
> > > are done allocating the memory. So I think in the case of SSD, when we
> > > stall waiting for IO some processes get to exit and free up memory, so
> > > we need to do less swapping out in general because the processes are
> > > more serialized. With zswap, all processes try to access memory at the
> > > same time so the required amount of memory at any given point is
> > > higher, leading to more thrashing.
> > >
> > > I suggested keeping the memory allocated for a long time to even the
> > > playing field, or we can make the processes keep looping and accessing
> > > the memory (or part of it) for a while.
> > >
> > > That being said, I think this may be a signal that the memory.high
> > > throttling is not performing as expected in the zswap case. Not sure
> > > tbh, but I don't think SSD swap should perform better than zswap in
> > > that case.
> >
> > Yeah something is fishy there. That said, the benchmarking in v4 is wack:
> >
> > 1. We use lz4, which has a really poor compression factor.
> >
> > 2. The swapfile is really small, so we occasionally see problems with
> > swap allocation failure.
> >
> > Both of these factors affect benchmarking validity and stability a
> > lot. I think in this version's benchmarks, with zstd as the software
> > compressor + a much larger swapfile (albeit on top of a ZRAM block
> > device), we no longer see memory.high violation, even at a lower
> > memory.high value...? The performance number is wack indeed - not a
> > lot of values in the case 2 section.
> 
> But when we use zram we are essentially comparing two swap mechanisms
> compressing mTHPs page by page, with the only difference being that
> zram does not account the memory. For this to have any value imo it
> should be on an SSD to at least provide the value of being a practical
> sanity check as you mentioned earlier. In its current form I don't
> think it's providing any value.

Just posted data today with SSD and longer running usemem processes,
that should hopefully better quantify the benefit of zswap-mTHP.

Thanks,
Kanchana