linux-kernel - Re: [PATCH] mm: introduce kv[mz]alloc helpers

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Message-ID: <20170102160249.GA11635@dhcp22.suse.cz>
Date:   Mon, 2 Jan 2017 17:02:50 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Joe Perches <joe@...ches.com>
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>, kvm@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org, linux-ext4@...r.kernel.org,
        Anatoly Stepanov <astepanov@...udlinux.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger@...ger.ca>
Subject: Re: [PATCH] mm: introduce kv[mz]alloc helpers

On Mon 02-01-17 07:55:22, Joe Perches wrote:
> On Mon, 2017-01-02 at 14:37 +0100, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@...e.com>
> > 
> > Using kmalloc with the vmalloc fallback for larger allocations is a
> > common pattern in the kernel code. Yet we do not have any common helper
> > for that and so users have invented their own helpers. Some of them are
> > really creative when doing so. Let's just add kv[mz]alloc and make sure
> > it is implemented properly. This implementation makes sure to not make
> > a large memory pressure for > PAGE_SZE requests (__GFP_NORETRY) and also
> > to not warn about allocation failures. This also rules out the OOM
> > killer as the vmalloc is a more approapriate fallback than a disruptive
> > user visible action.
> > 
> > This patch also changes some existing users and removes helpers which
> > are specific for them. In some cases this is not possible (e.g.
> > ext4_kvmalloc, libcfs_kvzalloc, __aa_kvmalloc) because those seems to be
> > broken and require GFP_NO{FS,IO} context which is not vmalloc compatible
> > in general (note that the page table allocation is GFP_KERNEL). Those
> > need to be fixed separately.
> > 
> > apparmor has already claimed kv[mz]alloc so remove those and use
> > __aa_kvmalloc instead to prevent from the naming clashes.
> 
> I have no real objection but perhaps this would
> be better done as 3 or more patches
> 
> o rename apparmor uses
> o introduce generic
> o conversions to generic

Whatever maintainers of the respective code prefer. I usually prefer to
have newly introduced functions along with their users so that it is
clear how they are used. The patch doesn't seem to be too large
either...
-- 
Michal Hocko
SUSE Labs