Re: [PATCHv11 2/4] zbud: add to mm/

From: Rik van Riel
Date: Thu May 16 2013 - 11:31:17 EST

On 05/13/2013 08:40 AM, Seth Jennings wrote:
zbud is an special purpose allocator for storing compressed pages. It is
designed to store up to two compressed pages per physical page. While this
design limits storage density, it has simple and deterministic reclaim
properties that make it preferable to a higher density approach when reclaim
will be used.

zbud works by storing compressed pages, or "zpages", together in pairs in a
single memory page called a "zbud page". The first buddy is "left
justifed" at the beginning of the zbud page, and the last buddy is "right
justified" at the end of the zbud page. The benefit is that if either
buddy is freed, the freed buddy space, coalesced with whatever slack space
that existed between the buddies, results in the largest possible free region
within the zbud page.

zbud also provides an attractive lower bound on density. The ratio of zpages
to zbud pages can not be less than 1. This ensures that zbud can never "do
harm" by using more pages to store zpages than the uncompressed zpages would
have used on their own.

This patch adds zbud to mm/ for later use by zswap.

Signed-off-by: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx>

Acked-by: Rik van Riel <riel@xxxxxxxxxx>

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