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

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Message-ID: <86cabb7a-1756-4d12-7ba4-776f66f6bb86@redhat.com>
Date:   Thu, 8 Dec 2016 14:00:20 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.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>,
        Anatoly Stepanov <astepanov@...udlinux.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "Theodore Ts'o" <tytso@....edu>, kvm@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org
Subject: Re: [RFC PATCH] mm: introduce kv[mz]alloc helpers

Am 08.12.2016 um 11:33 schrieb Michal Hocko:
> 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.
>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Mike Snitzer <snitzer@...hat.com>
> Cc: dm-devel@...hat.com
> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> Cc: "Theodore Ts'o" <tytso@....edu>
> Cc: kvm@...r.kernel.org
> Cc: linux-ext4@...r.kernel.org
> Cc: linux-f2fs-devel@...ts.sourceforge.net
> Cc: linux-security-module@...r.kernel.org
> Signed-off-by: Michal Hocko <mhocko@...e.com>

I remember yet another similar user in arch/s390/kvm/kvm-s390.c
-> kvm_s390_set_skeys()

...
keys = kmalloc_array(args->count, sizeof(uint8_t),
                      GFP_KERNEL | __GFP_NOWARN);
if (!keys)
         vmalloc(sizeof(uint8_t) * args->count);
...

would kvmalloc_array make sense? (it would even make the code here
less error prone and better to read)

-- 

David