Messages in this thread | | | Date | Sat, 13 Mar 2021 21:10:31 -0800 | From | Chris Goldsworthy <> | Subject | Re: [PATCH v3 2/3] mm: disable LRU pagevec during the migration temporarily |
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On 2021-03-11 14:41, Chris Goldsworthy wrote: > On 2021-03-10 08:14, Minchan Kim wrote: >> LRU pagevec holds refcount of pages until the pagevec are drained. >> It could prevent migration since the refcount of the page is greater >> than the expection in migration logic. To mitigate the issue, >> callers of migrate_pages drains LRU pagevec via migrate_prep or >> lru_add_drain_all before migrate_pages call. >> >> However, it's not enough because pages coming into pagevec after the >> draining call still could stay at the pagevec so it could keep >> preventing page migration. Since some callers of migrate_pages have >> retrial logic with LRU draining, the page would migrate at next trail >> but it is still fragile in that it doesn't close the fundamental race >> between upcoming LRU pages into pagvec and migration so the migration >> failure could cause contiguous memory allocation failure in the end. >> >> To close the race, this patch disables lru caches(i.e, pagevec) >> during ongoing migration until migrate is done. >> >> Since it's really hard to reproduce, I measured how many times >> migrate_pages retried with force mode(it is about a fallback to a >> sync migration) with below debug code. >> >> int migrate_pages(struct list_head *from, new_page_t get_new_page, >> .. >> .. >> >> if (rc && reason == MR_CONTIG_RANGE && pass > 2) { >> printk(KERN_ERR, "pfn 0x%lx reason %d\n", page_to_pfn(page), >> rc); >> dump_page(page, "fail to migrate"); >> } >> >> The test was repeating android apps launching with cma allocation >> in background every five seconds. Total cma allocation count was >> about 500 during the testing. With this patch, the dump_page count >> was reduced from 400 to 30. >> >> The new interface is also useful for memory hotplug which currently >> drains lru pcp caches after each migration failure. This is rather >> suboptimal as it has to disrupt others running during the operation. >> With the new interface the operation happens only once. This is also >> in >> line with pcp allocator cache which are disabled for the offlining as >> well. >> >> Signed-off-by: Minchan Kim <minchan@kernel.org> >> --- > > Hi Minchan, > > This all looks good to me - feel free to add a Reviewed-by from me. > > Thanks, > > Chris. Should have added:
Reviewed-by: Chris Goldsworthy <cgoldswo@codeaurora.org> -- The Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
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