Re: [PATCH v4] mm: Enable suspend-only swap spaces

From: Pavel Machek <pavel@ucw.cz>
To: Evan Green <evgreen@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	David Hildenbrand <david@redhat.com>,
	Michal Hocko <mhocko@suse.com>,
	linux-api@vger.kernel.org, Alex Shi <alexs@kernel.org>,
	Alistair Popple <apopple@nvidia.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Miaohe Lin <linmiaohe@huawei.com>,
	Minchan Kim <minchan@kernel.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org
Subject: Re: [PATCH v4] mm: Enable suspend-only swap spaces
Date: Tue, 17 Aug 2021 20:32:33 +0200	[thread overview]
Message-ID: <20210817183233.GA14518@amd> (raw)
In-Reply-To: <CAE=gft6LmTKx2JHAj7GBmph_1BrioXhmtn_xQEHtRhK+tPa6qw@mail.gmail.com>

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Hi!

> > > > Pavel just mentioned uswsusp, and I wonder if it would be a possible
> > > > alternative to this patch.
> > >
> > > I think you're right that it would be possible to isolate the
> > > hibernate image with uswsusp if you avoid using the SNAPSHOT_*SWAP*
> > > ioctls. But I'd expect performance to suffer noticeably, since now
> > > every page is making a round trip out to usermode and back. I'd still
> > > very much use the HIBERNATE_ONLY flag if it were accepted, I think
> > > there's value to it.
> >
> > The uswsusp option makes your patch a performance optimization rather
> > than a feature-add.  And we do like to see quantitative testing results
> > when considering a performance optimization.  Especially when the
> > performance optimization is a bit icky, putting special-case testing
> > all over the place, maintenance cost, additional testing effort, etc.
> >
> > I do think that diligence demands that we quantify the difference.  Is
> > this a thing you can help with?
> 
> I'm wrong about the performance. Uswsusp is just as fast, and possibly
> faster in my use case than kernel-driven hibernate. What's more,
> uswsusp also helps me solve several additional problems I hadn't
> tackled yet that were looming in front of me. Thanks all for your
> patience and thoughtful review on this.

Great to see uswsusp being used :-).

Thanks,
								Pavel
-- 
http://www.livejournal.com/~pavelmachek

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