linux-kernel - Re: [PATCH v4] mm: don't be stuck to rmap lock on reclaim path

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: <20220511190523.7d159b2e9caccbf13469e74e@linux-foundation.org>
Date:   Wed, 11 May 2022 19:05:23 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        John Dias <joaodias@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Martin Liu <liumartin@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v4] mm: don't be stuck to rmap lock on reclaim path

On Wed, 11 May 2022 15:57:09 -0700 Minchan Kim <minchan@...nel.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 ;)