Messages in this thread | | | Date | Thu, 25 Jun 2015 20:56:48 +0200 | From | Vlastimil Babka <> | Subject | Re: [RFC PATCH 00/10] redesign compaction algorithm |
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On 25.6.2015 20:14, Joonsoo Kim wrote: >> The long-term success rate of fragmentation avoidance depends on >> > minimsing the number of UNMOVABLE allocation requests that use a >> > pageblock belonging to another migratetype. Once such a fallback occurs, >> > that pageblock potentially can never be used for a THP allocation again. >> > >> > Lets say there is an unmovable pageblock with 500 free pages in it. If >> > the freepage scanner uses that pageblock and allocates all 500 free >> > pages then the next unmovable allocation request needs a new pageblock. >> > If one is not completely free then it will fallback to using a >> > RECLAIMABLE or MOVABLE pageblock forever contaminating it. > Yes, I can imagine that situation. But, as I said above, we already use > non-movable pageblock for migration scanner. While unmovable > pageblock with 500 free pages fills, some other unmovable pageblock > with some movable pages will be emptied. Number of freepage > on non-movable would be maintained so fallback doesn't happen.
There's nothing that guarantees that the migration scanner will be emptying unmovable pageblock, or am I missing something? Worse, those pageblocks would be marked to skip by the free scanner if it isolated free pages from them, so migration scanner would skip them.
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