Currently when we handle writeback in fuse, we allocate and copy data to a temporary folio in order to mitigate the following deadlock scenario that may arise if reclaim waits on writeback to complete: * single-threaded FUSE server is in the middle of handling a request that needs a memory allocation * memory allocation triggers direct reclaim * direct reclaim waits on a folio under writeback * the FUSE server can't write back the folio since it's stuck in direct reclaim (more details can be found here [1]) The first patch adds a AS_NO_WRITEBACK_RECLAIM flag to "enum mapping_flags" to indicate that reclaim when in writeback should be skipped for filesystems with this flag set. More details can be found in the commit message of the first patch, but this only actually affects the case of legacy cgroupv1 when it encounters a folio that already has the reclaim flag set (in the other cases, we already skip reclaim when in writeback). Doing so allows us to get rid of needing to allocate and copy over pages to a temporary folio when handling writeback in fuse (2nd patch). Benchmarks can be found in commit message of the 2nd patch. Thanks, Joanne [1] https://lore.kernel.org/linux-kernel/495d2400-1d96-4924-99d3-8b2952e05fc3@xxxxxxxxxxxxxxxxx/ v1: https://lore.kernel.org/linux-fsdevel/20241011223434.1307300-1-joannelkoong@xxxxxxxxx/T/#t Changes from v1 -> v2: * Have flag in "enum mapping_flags" instead of creating asop_flags (Shakeel) * Set fuse inodes to use AS_NO_WRITEBACK_RECLAIM (Shakeel) Joanne Koong (2): mm: skip reclaiming folios in writeback contexts that may trigger deadlock fuse: remove tmp folio for writebacks and internal rb tree fs/fuse/file.c | 322 ++++------------------------------------ include/linux/pagemap.h | 11 ++ mm/vmscan.c | 6 +- 3 files changed, 43 insertions(+), 296 deletions(-) -- 2.43.5
