Hello, After six years, prompted by recent 0-day reports of performance issues with orphan list handling [1], I'm sending a third revision of my series to speed up orphan inode handling in ext4. Orphan inode handling in ext4 is a bottleneck for workloads which heavily excercise truncate / unlink of small files as they contend on global s_orphan_mutex (when you have fast enough storage). This patch set implements new way of handling orphan inodes - instead of using a linked list, we store inode numbers of orphaned inodes in a file which is possible to implement in a more scalable manner than linked list manipulations. See description of patch 3/4 for more details. The patch set achieves significant gains both for a micro benchmark stressing orphan inode handling (truncating file byte-by-byte, several threads in parallel) and for reaim creat_clo workload. I'm happy for any review, thoughts, ideas about the patches. I have also implemented full support in e2fsprogs which I'll send separately. Honza [1] https://lore.kernel.org/lkml/20210227120804.GB22871@xsang-OptiPlex-9020/ Changes since v2: * Updated some comments * Rebased onto 5.13-rc5 * Change orphan file inode from a fixed inode number to inode number stored in the superblock Changes since v1: * orphan blocks have now magic numbers * split out orphan handling to a separate source file * some smaller updates according to review
