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

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Date:   Tue, 24 Sep 2019 23:19:29 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>, dsterba@...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 9/23/19 7:51 PM, Darrick J. Wong wrote:
> 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.

I think it's a big fail of kmalloc API that you have to do that, and
especially with vmalloc, which has the overhead of setting up page
tables, and it's a waste for allocation requests smaller than page size.
I wish we could have nice things.