Messages in this thread | | | Date | Thu, 04 Sep 2008 16:59:44 +0900 | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 4/4] capture pages freed during direct reclaim for allocation by the reclaimer |
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> When a process enters direct reclaim it will expend effort identifying > and releasing pages in the hope of obtaining a page. However as these > pages are released asynchronously there is every possibility that the > pages will have been consumed by other allocators before the reclaimer > gets a look in. This is particularly problematic where the reclaimer is > attempting to allocate a higher order page. It is highly likely that > a parallel allocation will consume lower order constituent pages as we > release them preventing them coelescing into the higher order page the > reclaimer desires. > > This patch set attempts to address this for allocations above > ALLOC_COSTLY_ORDER by temporarily collecting the pages we are releasing > onto a local free list. Instead of freeing them to the main buddy lists, > pages are collected and coelesced on this per direct reclaimer free list. > Pages which are freed by other processes are also considered, where they > coelesce with a page already under capture they will be moved to the > capture list. When pressure has been applied to a zone we then consult > the capture list and if there is an appropriatly sized page available > it is taken immediatly and the remainder returned to the free pool. > Capture is only enabled when the reclaimer's allocation order exceeds > ALLOC_COSTLY_ORDER as free pages below this order should naturally occur > in large numbers following regular reclaim.
Hi Andy,
I like almost part of your patch. (at least, I can ack patch 1/4 - 3/4)
So, I worry about OOM risk. Can you remember desired page size to capture list (or any other location)? if possible, __capture_on_page can avoid to capture unnecessary pages.
So, if __capture_on_page() can make desired size page by buddy merging, it can free other pages on capture_list.
In worst case, shrink_zone() is called by very much process at the same time. Then, if each process doesn't back few pages, very many pages doesn't be backed.
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