mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations
After the previous patch, we can distinguish costly allocations that should be really lightweight, such as THP page faults, with __GFP_NORETRY. This means we don't need to recognize khugepaged allocations via PF_KTHREAD anymore. We can also change THP page faults in areas where madvise(MADV_HUGEPAGE) was used to try as hard as khugepaged, as the process has indicated that it benefits from THP's and is willing to pay some initial latency costs. We can also make the flags handling less cryptic by distinguishing GFP_TRANSHUGE_LIGHT (no reclaim at all, default mode in page fault) from GFP_TRANSHUGE (only direct reclaim, khugepaged default). Adding __GFP_NORETRY or __GFP_KSWAPD_RECLAIM is done where needed. The patch effectively changes the current GFP_TRANSHUGE users as follows: * get_huge_zero_page() - the zero page lifetime should be relatively long and it's shared by multiple users, so it's worth spending some effort on it. We use GFP_TRANSHUGE, and __GFP_NORETRY is not added. This also restores direct reclaim to this allocation, which was unintentionally removed by commit e4a49efe4e7e ("mm: thp: set THP defrag by default to madvise and add a stall-free defrag option") * alloc_hugepage_khugepaged_gfpmask() - this is khugepaged, so latency is not an issue. So if khugepaged "defrag" is enabled (the default), do reclaim via GFP_TRANSHUGE without __GFP_NORETRY. We can remove the PF_KTHREAD check from page alloc. As a side-effect, khugepaged will now no longer check if the initial compaction was deferred or contended. This is OK, as khugepaged sleep times between collapsion attempts are long enough to prevent noticeable disruption, so we should allow it to spend some effort. * migrate_misplaced_transhuge_page() - already was masking out __GFP_RECLAIM, so just convert to GFP_TRANSHUGE_LIGHT which is equivalent. * alloc_hugepage_direct_gfpmask() - vma's with VM_HUGEPAGE (via madvise) are now allocating without __GFP_NORETRY. Other vma's keep using __GFP_NORETRY if direct reclaim/compaction is at all allowed (by default it's allowed only for madvised vma's). The rest is conversion to GFP_TRANSHUGE(_LIGHT). [mhocko@suse.com: suggested GFP_TRANSHUGE_LIGHT] Link: http://lkml.kernel.org/r/20160721073614.24395-7-vbabka@suse.czSigned-off-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Mel Gorman <mgorman@techsingularity.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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