From: Yosry Ahmed <yosryahmed@google.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Seth Jennings <sjenning@redhat.com>,
Dan Streetman <ddstreet@ieee.org>,
Vitaly Wool <vitaly.wool@konsulko.com>,
Nhat Pham <nphamcs@gmail.com>,
Domenico Cerasuolo <cerasuolodomenico@gmail.com>,
Yu Zhao <yuzhao@google.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: zswap: support exclusive loads
Date: Wed, 7 Jun 2023 09:33:34 -0700 [thread overview]
Message-ID: <CAJD7tkbHHVJfbybP0gqHGPp9J2t34-1NC0np6PgMdfxLmX-kpg@mail.gmail.com> (raw)
In-Reply-To: <20230607141357.GA338934@cmpxchg.org>
On Wed, Jun 7, 2023 at 7:13 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> On Tue, May 30, 2023 at 09:02:51PM +0000, Yosry Ahmed wrote:
> > @@ -46,6 +46,19 @@ config ZSWAP_DEFAULT_ON
> > The selection made here can be overridden by using the kernel
> > command line 'zswap.enabled=' option.
> >
> > +config ZSWAP_EXCLUSIVE_LOADS
> > + bool "Invalidate zswap entries when pages are loaded"
> > + depends on ZSWAP
> > + help
> > + If selected, when a page is loaded from zswap, the zswap entry is
> > + invalidated at once, as opposed to leaving it in zswap until the
> > + swap entry is freed.
> > +
> > + This avoids having two copies of the same page in memory
> > + (compressed and uncompressed) after faulting in a page from zswap.
> > + The cost is that if the page was never dirtied and needs to be
> > + swapped out again, it will be re-compressed.
> > +
> > choice
> > prompt "Default compressor"
> > depends on ZSWAP
> > diff --git a/mm/frontswap.c b/mm/frontswap.c
> > index 279e55b4ed87..e5d6825110f4 100644
> > --- a/mm/frontswap.c
> > +++ b/mm/frontswap.c
> > @@ -216,8 +216,13 @@ int __frontswap_load(struct page *page)
> >
> > /* Try loading from each implementation, until one succeeds. */
> > ret = frontswap_ops->load(type, offset, page);
> > - if (ret == 0)
> > + if (ret == 0) {
> > inc_frontswap_loads();
> > + if (frontswap_ops->exclusive_loads) {
> > + SetPageDirty(page);
> > + __frontswap_clear(sis, offset);
> > + }
> > + }
> > return ret;
>
> This would be a much more accessible feature (distro kernels,
> experimenting, adapting to different workloads) if it were runtime
> switchable.
>
> That should be possible, right? As long as frontswap and zswap are
> coordinated, this can be done on a per-entry basis:
>
> exclusive = READ_ONCE(frontswap_ops->exclusive_loads);
> ret = frontswap_ops->load(type, offset, page, exclusive);
> if (ret == 0) {
> if (exclusive) {
> SetPageDirty(page);
> __frontswap_clear(sis, offset);
> }
> }
Sure, I can do that. My thought was that this isn't something that
someone usually wants to change at runtime, but at least for
experimentation, it does make things a lot easier. I can add a zswap
module parameter.
I am guessing for consistency with other zswap settings and for
convenience, I can leave the config option to set the default value
with, aka CONFIG_ZSWAP_EXCLUSIVE_LOADS_DEFAULT_ON or something. Does
this make sense?
prev parent reply other threads:[~2023-06-07 16:34 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-30 21:02 [PATCH] mm: zswap: support exclusive loads Yosry Ahmed
2023-05-30 21:15 ` Andrew Morton
2023-05-30 21:20 ` Yosry Ahmed
2023-05-30 23:54 ` Johannes Weiner
2023-05-30 23:56 ` Yosry Ahmed
2023-05-31 6:00 ` Christoph Hellwig
2023-06-07 14:13 ` Johannes Weiner
2023-06-07 16:33 ` Yosry Ahmed [this message]
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