From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Chuck Lever <chuck.lever@oracle.com>,
Mel Gorman <mgorman@suse.de>,
Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Jakub Kicinski <kuba@kernel.org>,
brouer@redhat.com,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: alloc_pages_bulk()
Date: Mon, 22 Feb 2021 12:42:46 +0100 [thread overview]
Message-ID: <20210222124246.690414a2@carbon> (raw)
In-Reply-To: <20210222094256.GH3697@techsingularity.net>
On Mon, 22 Feb 2021 09:42:56 +0000
Mel Gorman <mgorman@techsingularity.net> wrote:
> On Mon, Feb 15, 2021 at 05:10:38PM +0100, Jesper Dangaard Brouer wrote:
> >
> > On Mon, 15 Feb 2021 12:00:56 +0000
> > Mel Gorman <mgorman@techsingularity.net> wrote:
> >
> > > On Thu, Feb 11, 2021 at 01:26:28PM +0100, Jesper Dangaard Brouer wrote:
> > [...]
> > >
> > > > I also suggest the API can return less pages than requested. Because I
> > > > want to to "exit"/return if it need to go into an expensive code path
> > > > (like buddy allocator or compaction). I'm assuming we have a flags to
> > > > give us this behavior (via gfp_flags or alloc_flags)?
> > > >
> > >
> > > The API returns the number of pages returned on a list so policies
> > > around how aggressive it should be allocating the requested number of
> > > pages could be adjusted without changing the API. Passing in policy
> > > requests via gfp_flags may be problematic as most (all?) bits are
> > > already used.
> >
> > Well, I was just thinking that I would use GFP_ATOMIC instead of
> > GFP_KERNEL to "communicate" that I don't want this call to take too
> > long (like sleeping). I'm not requesting any fancy policy :-)
> >
>
> The NFS use case requires opposite semantics
> -- it really needs those allocations to succeed
> https://lore.kernel.org/r/161340498400.7780.962495219428962117.stgit@klimt.1015granger.net.
Sorry, but that is not how I understand the code.
The code is doing exactly what I'm requesting. If the alloc_pages_bulk()
doesn't return expected number of pages, then check if others need to
run. The old code did schedule_timeout(msecs_to_jiffies(500)), while
Chuck's patch change this to ask for cond_resched(). Thus, it tries to
avoid blocking the CPU for too long (when allocating many pages).
And the nfsd code seems to handle that the code can be interrupted (via
return -EINTR) via signal_pending(current). Thus, the nfsd code seems
to be able to handle if the page allocations failed.
> I've asked what code it's based on as it's not 5.11 and I'll iron that
> out first.
>
> Then it might be clearer what the "can fail" semantics should look like.
> I think it would be best to have pairs of patches where the first patch
> adjusts the semantics of the bulk allocator and the second adds a user.
> That will limit the amount of code code carried in the implementation.
> When the initial users are in place then the implementation can be
> optimised as the optimisations will require significant refactoring and
> I not want to refactor multiple times.
I guess, I should try to code-up the usage in page_pool.
What is the latest patch for adding alloc_pages_bulk() ?
The nfsd code (svc_alloc_arg) is called in a context where it can
sleep, and thus use GFP_KERNEL. In most cases the page_pool will be
called with GFP_ATOMIC. I don't think I/page_pool will retry the call
like Chuck did, as I cannot (re)schedule others to run.
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
next prev parent reply other threads:[~2021-02-22 11:43 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <2A0C36E7-8CB0-486F-A8DB-463CA28C5C5D@oracle.com>
2021-02-08 17:50 ` Fwd: alloc_pages_bulk() Chuck Lever
2021-02-09 10:31 ` alloc_pages_bulk() Jesper Dangaard Brouer
2021-02-09 13:37 ` alloc_pages_bulk() Chuck Lever
2021-02-09 17:27 ` alloc_pages_bulk() Vlastimil Babka
2021-02-10 9:51 ` alloc_pages_bulk() Christoph Hellwig
2021-02-10 8:41 ` alloc_pages_bulk() Mel Gorman
2021-02-10 11:41 ` alloc_pages_bulk() Jesper Dangaard Brouer
2021-02-10 13:07 ` alloc_pages_bulk() Mel Gorman
2021-02-10 22:58 ` alloc_pages_bulk() Chuck Lever
2021-02-11 9:12 ` alloc_pages_bulk() Mel Gorman
2021-02-11 12:26 ` alloc_pages_bulk() Jesper Dangaard Brouer
2021-02-15 12:00 ` alloc_pages_bulk() Mel Gorman
2021-02-15 16:10 ` alloc_pages_bulk() Jesper Dangaard Brouer
2021-02-22 9:42 ` alloc_pages_bulk() Mel Gorman
2021-02-22 11:42 ` Jesper Dangaard Brouer [this message]
2021-02-22 14:08 ` alloc_pages_bulk() Mel Gorman
2021-02-11 16:20 ` alloc_pages_bulk() Chuck Lever
2021-02-15 12:06 ` alloc_pages_bulk() Mel Gorman
2021-02-15 16:00 ` alloc_pages_bulk() Chuck Lever
2021-02-22 20:44 ` alloc_pages_bulk() Jesper Dangaard Brouer
2021-02-09 22:01 ` Fwd: alloc_pages_bulk() Matthew Wilcox
2021-02-09 22:55 ` alloc_pages_bulk() Chuck Lever
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