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SubjectRe: [PATCH 5/8] Fragmentation Avoidance V17: 005_fallback
On Tue, Oct 11, 2005 at 04:12:47PM +0100, Mel Gorman wrote:
> This patch implements fallback logic. In the event there is no 2^(MAX_ORDER-1)
> blocks of pages left, this will help the system decide what list to use. The
> highlights of the patch are;
>
> o Define a RCLM_FALLBACK type for fallbacks
> o Use a percentage of each zone for fallbacks. When a reserved pool of pages
> is depleted, it will try and use RCLM_FALLBACK before using anything else.
> This greatly reduces the amount of fallbacks causing fragmentation without
> needing complex balancing algorithms

I'm having a little trouble seeing how adding a new type (RCLM_FALLBACK)
helps. Seems to me that pages put into the RCLM_FALLBACK area would have
gone to the global free list and available to anyone. I must be missing
something here.

> +int fallback_allocs[RCLM_TYPES][RCLM_TYPES+1] = {
> + {RCLM_NORCLM, RCLM_FALLBACK, RCLM_KERN, RCLM_USER, RCLM_TYPES},
> + {RCLM_KERN, RCLM_FALLBACK, RCLM_NORCLM, RCLM_USER, RCLM_TYPES},
> + {RCLM_USER, RCLM_FALLBACK, RCLM_NORCLM, RCLM_KERN, RCLM_TYPES},
> + {RCLM_FALLBACK, RCLM_NORCLM, RCLM_KERN, RCLM_USER, RCLM_TYPES}

Do you really need that last line? Can an allocation of type RCLM_FALLBACK
realy be made?

--
Mike
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