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Date: Wed, 9 Oct 2013 12:16:17 -0500
From: Seth Jennings <spartacus06@gmail.com>
Subject: Re: [PATCH v3 5/6] zswap: replace tree in zswap with radix tree in
 zbud
Message-ID: <20131009171617.GA21057@variantweb.net>
References: <1381238980-2491-1-git-send-email-k.kozlowski@samsung.com>
 <1381238980-2491-6-git-send-email-k.kozlowski@samsung.com>
 <20131009153022.GB5406@variantweb.net>
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To: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>, Bob Liu <bob.liu@oracle.com>, Mel Gorman <mgorman@suse.de>, Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>, Marek Szyprowski <m.szyprowski@samsung.com>, Tomasz Stanislawski <t.stanislaws@samsung.com>, Kyungmin Park <kyungmin.park@samsung.com>, Dave Hansen <dave.hansen@intel.com>, Minchan Kim <minchan@kernel.org>

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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