Re: [PATCH] mm: introduce kv[mz]alloc helpers

From: Michal Hocko <mhocko@kernel.org>
To: Joe Perches <joe@perches.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	David Rientjes <rientjes@google.com>,
	Mel Gorman <mgorman@suse.de>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	kvm@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net,
	linux-security-module@vger.kernel.org,
	linux-ext4@vger.kernel.org,
	Anatoly Stepanov <astepanov@cloudlinux.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Mike Snitzer <snitzer@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"Theodore Ts'o" <tytso@mit.edu>,
	Andreas Dilger <adilger@dilger.ca>
Subject: Re: [PATCH] mm: introduce kv[mz]alloc helpers
Date: Mon, 2 Jan 2017 17:02:50 +0100	[thread overview]
Message-ID: <20170102160249.GA11635@dhcp22.suse.cz> (raw)
In-Reply-To: <1483372522.1955.20.camel@perches.com>

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@suse.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