linux-kernel - Re: [PATCH v3 5/6] zswap: replace tree in zswap with radix tree in zbud

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Date:	Wed, 9 Oct 2013 12:16:17 -0500
From:	Seth Jennings <spartacus06@...il.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bob Liu <bob.liu@...cle.com>, Mel Gorman <mgorman@...e.de>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Tomasz Stanislawski <t.stanislaws@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH v3 5/6] zswap: replace tree in zswap with radix tree in
 zbud

On Wed, Oct 09, 2013 at 10:30:22AM -0500, Seth Jennings wrote:
> In my approach, I was also looking at allowing the zbud pools to use
> HIGHMEM pages, since the handle is no longer an address.  This requires
> the pages that are being mapped to be kmapped (atomic) which will
> disable preemption.  This isn't an additional overhead since the
> map/unmap corresponds with a compress/decompress operation at the zswap
> level which uses per-cpu variables that disable preemption already.

On second though, lets not mess with the HIGHMEM page support for now.
Turns out it is tricker than I thought since the unbuddied lists are
linked through the zbud header stored in the page.  But we can still
disable preemption to allow per-cpu tracking of the current mapping and
avoid a lookup (and races) in zbud_unmap().

Seth
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