From: "Paul E. McKenney" <paulmck@kernel.org>
To: Michal Hocko <mhocko@suse.com>
Cc: liam.howlett@oracle.com, willy@infradead.org,
walken.cr@gmail.com, hannes@cmpxchg.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: Memory allocation on speculative fastpaths
Date: Tue, 3 May 2022 09:39:05 -0700 [thread overview]
Message-ID: <20220503163905.GM1790663@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <YnFSfc8BR8CadOtw@dhcp22.suse.cz>
On Tue, May 03, 2022 at 06:04:13PM +0200, Michal Hocko wrote:
> On Tue 03-05-22 08:59:13, Paul E. McKenney wrote:
> > Hello!
> >
> > Just following up from off-list discussions yesterday.
> >
> > The requirements to allocate on an RCU-protected speculative fastpath
> > seem to be as follows:
> >
> > 1. Never sleep.
> > 2. Never reclaim.
> > 3. Leave emergency pools alone.
> >
> > Any others?
> >
> > If those rules suffice, and if my understanding of the GFP flags is
> > correct (ha!!!), then the following GFP flags should cover this:
> >
> > __GFP_NOMEMALLOC | __GFP_NOWARN
>
> GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_NOWARN
Ah, good point on GFP_NOWAIT, thank you!
> > Or is this just a fancy way of always returning NULL or some such? ;-)
>
> It could fail quite easily. We would also want to guarantee (by
> documenting I guess) that the page allocator never does anything that
> would depend or invoke rcu_synchronize or something like that.
The GPF_NOWAIT should rule out synchronize_rcu() and similar, correct?
> I believe this is the case currently.
Here is hoping! ;-)
Thanx, Paul
next prev parent reply other threads:[~2022-05-03 16:39 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-03 15:59 Paul E. McKenney
2022-05-03 16:04 ` Michal Hocko
2022-05-03 16:39 ` Paul E. McKenney [this message]
2022-05-03 18:28 ` Matthew Wilcox
2022-05-03 23:15 ` Suren Baghdasaryan
2022-05-03 23:45 ` Michal Hocko
2022-05-04 0:22 ` Matthew Wilcox
2022-05-04 16:23 ` Johannes Weiner
2022-05-24 20:37 ` Vlastimil Babka
2022-05-25 13:12 ` Johannes Weiner
2022-05-04 8:20 ` Michel Lespinasse
2022-05-04 16:52 ` Matthew Wilcox
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220503163905.GM1790663@paulmck-ThinkPad-P17-Gen-1 \
--to=paulmck@kernel.org \
--cc=hannes@cmpxchg.org \
--cc=liam.howlett@oracle.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@suse.com \
--cc=walken.cr@gmail.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox