linux-kernel - Re: [PATCH v2 2/2] mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two)

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Message-ID: <20190904064043.GA7578@ming.t460p>
Date:   Wed, 4 Sep 2019 14:40:44 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Christopher Lameter <cl@...ux.com>,
        Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Dave Chinner <david@...morbit.com>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        linux-btrfs@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm, sl[aou]b: guarantee natural alignment for
 kmalloc(power-of-two)

On Wed, Sep 04, 2019 at 07:19:33AM +0200, Christoph Hellwig wrote:
> On Tue, Sep 03, 2019 at 01:53:12PM -0700, Matthew Wilcox wrote:
> > > Its enabled in all full debug session as far as I know. Fedora for
> > > example has been running this for ages to find breakage in device drivers
> > > etc etc.
> > 
> > Are you telling me nobody uses the ramdisk driver on fedora?  Because
> > that's one of the affected drivers.
> 
> For pmem/brd misaligned memory alone doesn't seem to be the problem.
> Misaligned memory that cross a page barrier is.  And at least XFS
> before my log recovery changes only used kmalloc for smaller than
> page size allocation, so this case probably didn't hit.

BTW, does sl[aou]b guarantee that smaller than page size allocation via kmalloc()
won't cross page boundary any time?

Thanks,
Ming