linux-kernel - Re: [PATCH 0/6 v3] kvmalloc

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Message-ID: <20170124191716.GA23114@ast-mbp.thefacebook.com>
Date:   Tue, 24 Jan 2017 11:17:21 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Rientjes <rientjes@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Al Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Anatoly Stepanov <astepanov@...udlinux.com>,
        Andreas Dilger <adilger@...ger.ca>,
        Andreas Dilger <andreas.dilger@...el.com>,
        Anton Vorontsov <anton@...msg.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Colin Cross <ccross@...roid.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Sterba <dsterba@...e.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Hariprasad S <hariprasad@...lsio.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Dryomov <idryomov@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Oleg Drokin <oleg.drokin@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Santosh Raspatur <santosh@...lsio.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Theodore Ts'o <tytso@....edu>,
        Tom Herbert <tom@...bertland.com>,
        Tony Luck <tony.luck@...el.com>,
        "Yan, Zheng" <zyan@...hat.com>,
        Yishai Hadas <yishaih@...lanox.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH 0/6 v3] kvmalloc

On Tue, Jan 24, 2017 at 04:17:52PM +0100, Michal Hocko wrote:
> On Thu 12-01-17 16:37:11, Michal Hocko wrote:
> > Hi,
> > this has been previously posted as a single patch [1] but later on more
> > built on top. It turned out that there are users who would like to have
> > __GFP_REPEAT semantic. This is currently implemented for costly >64B
> > requests. Doing the same for smaller requests would require to redefine
> > __GFP_REPEAT semantic in the page allocator which is out of scope of
> > this series.
> > 
> > There are many open coded kmalloc with vmalloc fallback instances in
> > the tree.  Most of them are not careful enough or simply do not care
> > about the underlying semantic of the kmalloc/page allocator which means
> > that a) some vmalloc fallbacks are basically unreachable because the
> > kmalloc part will keep retrying until it succeeds b) the page allocator
> > can invoke a really disruptive steps like the OOM killer to move forward
> > which doesn't sound appropriate when we consider that the vmalloc
> > fallback is available.
> > 
> > As it can be seen implementing kvmalloc requires quite an intimate
> > knowledge if the page allocator and the memory reclaim internals which
> > strongly suggests that a helper should be implemented in the memory
> > subsystem proper.
> > 
> > Most callers I could find have been converted to use the helper instead.
> > This is patch 5. There are some more relying on __GFP_REPEAT in the
> > networking stack which I have converted as well but considering we do
> > not have a support for __GFP_REPEAT for requests smaller than 64kB I
> > have marked it RFC.
> 
> Are there any more comments? I would really appreciate to hear from
> networking folks before I resubmit the series.

while this patchset was baking the bpf side switched to use bpf_map_area_alloc()
which fixes the issue with missing __GFP_NORETRY that we had to fix quickly.
See commit d407bd25a204 ("bpf: don't trigger OOM killer under pressure with map alloc")
it covers all kmalloc/vmalloc pairs instead of just one place as in this set.
So please rebase and switch bpf_map_area_alloc() to use kvmalloc().
Thanks