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As large folio adoption expanded acros= s > the kernel, CONFIG_TRANSPARENT_HUGEPAGE has become an overloaded > configuration option, sometimes used as a proxy for large folio support= > [1][2][3]. > > This series is a part of the LPC talk[4], and I am sending the RFC > series to start the discussion. > > There are multiple solutions to solve this problem and this is one of > them with minimal changes. I plan on discussing possible other solution= s > at the talk. > > Based on my investigation, the only feature large folios depend on is > the THP splitting infrastructure. Either during truncation or memory > pressure when the large folio has to be split, then THP's splitting > infrastructure is used to split them into min order folio chunks. > > In this approach, we restrict the maximum order of the large folio to > minimum order to ensure we never use the splitting infrastructure when > THP is disabled. > > I disabled THP, and ran xfstests on XFS with 16k, 32k and 64k blocksize= s > and the changes seems to survive the test without any issues. But are large folios really created? IIUC, in do_sync_mmap_readahead(), when THP is disabled, force_thp_readah= ead is never set to true and later ra->order is set to 0. Oh, page_cache_ra_o= rder() later bumps new_order to mapping_min_folio_order(). So large folios are created there. I wonder if core-mm should move mTHP code out of CONFIG_TRANSPARENT_HUGEP= AGE and mTHP might just work. Hmm, folio split might need to be moved out of mm/huge_memory.c in that case. khugepaged should work for mTHP without CONFIG_TRANSPARENT_HUGEPAGE as well. OK, for anon folios, the changes mig= ht be more involved. > > Looking forward to some productive discussion. > > P.S: Thanks to Zi, David and willy for all the ideas they provided to > solve this problem. > > [1] https://lore.kernel.org/linux-mm/731d8b44-1a45-40bc-a274-8f39a7ae0f= 7f@lucifer.local/ > [2] https://lore.kernel.org/all/aGfNKGBz9lhuK1AF@casper.infradead.org/ > [3] https://lore.kernel.org/linux-ext4/20251110043226.GD2988753@mit.edu= / > [4] https://lpc.events/event/19/contributions/2139/ > > Pankaj Raghav (3): > filemap: set max order to be min order if THP is disabled > huge_memory: skip warning if min order and folio order are same in > split > blkdev: remove CONFIG_TRANSPARENT_HUGEPAGES dependency for LBS device= s > > include/linux/blkdev.h | 5 ----- > include/linux/huge_mm.h | 40 ++++++++-------------------------------- > include/linux/pagemap.h | 17 ++++++----------- > mm/memory.c | 41 +++++++++++++++++++++++++++++++++++++++++= > 4 files changed, 55 insertions(+), 48 deletions(-) > > > base-commit: e4c4d9892021888be6d874ec1be307e80382f431 > -- = > 2.50.1 Best Regards, Yan, Zi