On 10 Dec 2021, at 2:30, Eric Ren wrote: > Hi Zi Yan, > > On 2021/12/10 07:04, Zi Yan wrote: >> From: Zi Yan >> >> Hi all, >> >> This patchset tries to remove the MAX_ORDER - 1 alignment requirement for CMA >> and alloc_contig_range(). It prepares for my upcoming changes to make MAX_ORDER >> adjustable at boot time[1]. >> >> The MAX_ORDER - 1 alignment requirement comes from that alloc_contig_range() >> isolates pageblocks to remove free memory from buddy allocator but isolating >> only a subset of pageblocks within a page spanning across multiple pageblocks >> causes free page accounting issues. Isolated page might not be put into the >> right free list, since the code assumes the migratetype of the first pageblock >> as the whole free page migratetype. This is based on the discussion at [2]. >> >> To remove the requirement, this patchset: >> 1. still isolates pageblocks at MAX_ORDER - 1 granularity; > Then, unplug fails if either pageblock of the  MAX_ORDER - 1 page has unmovable page, right? Right. One of the optimizations mentioned is targeting this by passing the actual range instead of the MAX_ORDER-1 aligned range, so that has_unmovable_pages() will not give false positive, minimizing the isolation failure rates. > > Thanks, > Eric >> 2. but saves the pageblock migratetypes outside the specified range of >> alloc_contig_range() and restores them after all pages within the range >> become free after __alloc_contig_migrate_range(); >> 3. splits free pages spanning multiple pageblocks at the beginning and the end >> of the range and puts the split pages to the right migratetype free lists >> based on the pageblock migratetypes; >> 4. returns pages not in the range as it did before this patch. >> >> Isolation needs to happen at MAX_ORDER - 1 granularity, because otherwise >> 1) extra code is needed to detect pages (free, PageHuge, THP, or PageCompound) >> to make sure all pageblocks belonging to a single page are isolated together >> and later pageblocks outside the range need to have their migratetypes restored; >> or 2) extra logic will need to be added during page free time to split a free >> page with multi-migratetype pageblocks. >> >> Two optimizations might come later: >> 1. only check unmovable pages within the range instead of MAX_ORDER - 1 aligned >> range during isolation to increase successful rate of alloc_contig_range(). ^^^^^^^^^^^^^^ >> 2. make MIGRATE_ISOLATE a separate bit to avoid saving and restoring existing >> migratetypes before and after isolation respectively. >> >> Feel free to give comments and suggestions. Thanks. >> >> >> [1] https://lore.kernel.org/linux-mm/20210805190253.2795604-1-zi.yan@sent.com/ >> [2] https://lore.kernel.org/linux-mm/d19fb078-cb9b-f60f-e310-fdeea1b947d2@redhat.com/ >> >> >> Zi Yan (7): >> mm: page_alloc: avoid merging non-fallbackable pageblocks with others. >> mm: compaction: handle non-lru compound pages properly in >> isolate_migratepages_block(). >> mm: migrate: allocate the right size of non hugetlb or THP compound >> pages. >> mm: make alloc_contig_range work at pageblock granularity >> mm: cma: use pageblock_order as the single alignment >> drivers: virtio_mem: use pageblock size as the minimum virtio_mem >> size. >> arch: powerpc: adjust fadump alignment to be pageblock aligned. >> >> arch/powerpc/include/asm/fadump-internal.h | 4 +- >> drivers/virtio/virtio_mem.c | 6 +- >> include/linux/mmzone.h | 11 +- >> kernel/dma/contiguous.c | 2 +- >> mm/cma.c | 6 +- >> mm/compaction.c | 10 +- >> mm/migrate.c | 8 +- >> mm/page_alloc.c | 203 +++++++++++++++++---- >> 8 files changed, 196 insertions(+), 54 deletions(-) >> -- Best Regards, Yan, Zi