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

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Message-ID: <20170124151752.GO6867@dhcp22.suse.cz>
Date:   Tue, 24 Jan 2017 16:17:52 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     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>
Subject: Re: [PATCH 0/6 v3] kvmalloc

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.

Thanks!

> [1] http://lkml.kernel.org/r/20170102133700.1734-1-mhocko@kernel.org
> 

-- 
Michal Hocko
SUSE Labs