From: Andrew Morton <akpm@linux-foundation.org>
To: Minchan Kim <minchan@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, John Dias <joaodias@google.com>,
Tim Murray <timmurray@google.com>,
Matthew Wilcox <willy@infradead.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Martin Liu <liumartin@google.com>,
Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH v4] mm: don't be stuck to rmap lock on reclaim path
Date: Wed, 11 May 2022 19:05:23 -0700 [thread overview]
Message-ID: <20220511190523.7d159b2e9caccbf13469e74e@linux-foundation.org> (raw)
In-Reply-To: <Ynw/RRsEj33gq+Hf@google.com>
On Wed, 11 May 2022 15:57:09 -0700 Minchan Kim <minchan@kernel.org> wrote:
> >
> > Could we burn much CPU time pointlessly churning though the LRU? Could
> > it mess up aging decisions enough to be performance-affecting in any
> > workload?
>
> Yes, correct. However, we are already churning LRUs by several
> ways. For example, isolate and putback from LRU list for page
> migration from several sources(typical example is compaction)
> and trylock_page and sc->gfp_mask not allowing page to be
> reclaimed in shrink_page_list.
Well. "we're already doing a risky thing so it's OK to do more of that
thing"?
> >
> > Something else?
>
> One thing I am worry about was the granularity of the churning.
> Example above was page granuarity churning so might be execuse
> but this one is address space's churning, especically for file LRU
> (i_mmap_rwsem) which might cause too many rotating and live-lock
> in the end(keey rotating in small LRU with heavy memory pressure).
>
> If it could be a problem, maybe we use sc->priority to stop
> the skipping on a certain level of memory pressure.
>
> Any thought? Do we really need it?
Are we able to think of a test which might demonstrate any worst case?
Whip that up and see what the numbers say?
It's a bit of a drag, but if we don't do it, our users surely will ;)
next prev parent reply other threads:[~2022-05-12 2:05 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 21:54 Minchan Kim
2022-05-10 22:26 ` Johannes Weiner
2022-05-11 22:33 ` Andrew Morton
2022-05-11 22:57 ` Minchan Kim
2022-05-12 2:05 ` Andrew Morton [this message]
2022-05-12 19:55 ` Minchan Kim
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