linux-kernel - Re: [PATCH 10/10] percpu: add optimizations on allocation path for the bitmap allocator

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Date:   Mon, 17 Jul 2017 19:32:05 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Dennis Zhou <dennisz@...com>
Cc:     Christoph Lameter <cl@...ux.com>, kernel-team@...com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Dennis Zhou <dennisszhou@...il.com>
Subject: Re: [PATCH 10/10] percpu: add optimizations on allocation path for
 the bitmap allocator

On Sat, Jul 15, 2017 at 10:23:15PM -0400, Dennis Zhou wrote:
> From: "Dennis Zhou (Facebook)" <dennisszhou@...il.com>
> 
> This patch adds two optimizations to the allocation path. The first is
> to not consider a chunk if the requested allocation cannot fit in the
> chunk's contig_hint. The benefit is that this avoids unncessary scanning
> over a chunk as the assumption is memory pressure is high and creating a
> new chunk has minimal consequences. This may fail when the contig_hint
> has poor alignment, but again we fall back on the high memory pressure
> argument.
> 
> The second is just a fail-fast mechanism. When allocating, a offset is
> identified within a block and then scanning is used to see if it will
> fit. An offset should never be returned unless it is known to fit, so
> here we just bind the scanning to the size of a block.
> 
> Signed-off-by: Dennis Zhou <dennisszhou@...il.com>

Looks good to me and there's nothing wrong with these two
optimizations being in a separate patch but they might be too little
to help reviewing / debugging in any noticeable way.  It'd be great if
more significant parts can be separated out.  If not, this is fine
too.

Thanks.

-- 
tejun