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: <20190923175146.GT2229799@magnolia>
Date:   Mon, 23 Sep 2019 10:51:46 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     dsterba@...e.cz, Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Ming Lei <ming.lei@...hat.com>,
        Dave Chinner <david@...morbit.com>,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Hellwig <hch@....de>, 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, Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v2 2/2] mm, sl[aou]b: guarantee natural alignment for
 kmalloc(power-of-two)

On Mon, Sep 23, 2019 at 07:17:10PM +0200, David Sterba wrote:
> On Mon, Sep 23, 2019 at 06:36:32PM +0200, Vlastimil Babka wrote:
> > So if anyone thinks this is a good idea, please express it (preferably
> > in a formal way such as Acked-by), otherwise it seems the patch will be
> > dropped (due to a private NACK, apparently).

Oh, I didn't realize  ^^^^^^^^^^^^ that *some* of us are allowed the
privilege of gutting a patch via private NAK without any of that open
development discussion incovenience. <grumble>

As far as XFS is concerned I merged Dave's series that checks the
alignment of io memory allocations and falls back to vmalloc if the
alignment won't work, because I got tired of scrolling past the endless
discussion and bug reports and inaction spanning months.

Now this private NAK stuff helps me feel vindicated for merging it
despite my misgivings because now I can declare that "XFS will just work
around all the stupid broken sh*t it finds in the rest of the kernel".

--D

> As a user of the allocator interface in filesystem, I'd like to see a
> more generic way to address the alignment guarantees so we don't have to
> apply workarounds like 3acd48507dc43eeeb each time we find that we
> missed something. (Where 'missed' might be another sort of weird memory
> corruption hard to trigger.)
> 
> The workaround got applied because I was not sure about the timeframe of
> merge of this patch, also to remove pressure for merge in case there are
> more private acks and nacks to be sent. In the end I'd be fine with
> reverting the workaround in order to use the generic code again.
> 
> Thanks.