The patch titled Subject: seqlock: add raw_seqcount_try_begin has been added to the -mm mm-unstable branch. Its filename is seqlock-add-raw_seqcount_try_begin.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/seqlock-add-raw_seqcount_try_begin.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Suren Baghdasaryan <surenb@xxxxxxxxxx> Subject: seqlock: add raw_seqcount_try_begin Date: Fri, 22 Nov 2024 09:44:14 -0800 Add raw_seqcount_try_begin() to opens a read critical section of the given seqcount_t if the counter is even. This enables eliding the critical section entirely if the counter is odd, instead of doing the speculation knowing it will fail. Link: https://lkml.kernel.org/r/20241122174416.1367052-1-surenb@xxxxxxxxxx Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Christian Brauner <brauner@xxxxxxxxxx> Cc: David Howells <dhowells@xxxxxxxxxx> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx> Cc: Hillf Danton <hdanton@xxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> Cc: Mateusz Guzik <mjguzik@xxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx> Cc: Sourav Panda <souravpanda@xxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Wei Yang <richard.weiyang@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/seqlock.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) --- a/include/linux/seqlock.h~seqlock-add-raw_seqcount_try_begin +++ a/include/linux/seqlock.h @@ -319,6 +319,28 @@ SEQCOUNT_LOCKNAME(mutex, struct m }) /** + * raw_seqcount_try_begin() - begin a seqcount_t read critical section + * w/o lockdep and w/o counter stabilization + * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants + * + * Similar to raw_seqcount_begin(), except it enables eliding the critical + * section entirely if odd, instead of doing the speculation knowing it will + * fail. + * + * Useful when counter stabilization is more or less equivalent to taking + * the lock and there is a slowpath that does that. + * + * If true, start will be set to the (even) sequence count read. + * + * Return: true when a read critical section is started. + */ +#define raw_seqcount_try_begin(s, start) \ +({ \ + start = raw_read_seqcount(s); \ + !(start & 1); \ +}) + +/** * raw_seqcount_begin() - begin a seqcount_t read critical section w/o * lockdep and w/o counter stabilization * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants _ Patches currently in -mm which might be from surenb@xxxxxxxxxx are alloc_tag-fix-module-allocation-tags-populated-area-calculation.patch alloc_tag-fix-set_codetag_empty-when-config_mem_alloc_profiling_debug.patch seqlock-add-raw_seqcount_try_begin.patch mm-convert-mm_lock_seq-to-a-proper-seqcount.patch mm-introduce-mmap_lock_speculate_try_beginretry.patch mm-introduce-vma_start_read_locked_nested-helpers.patch mm-move-per-vma-lock-into-vm_area_struct.patch mm-mark-vma-as-detached-until-its-added-into-vma-tree.patch mm-make-vma-cache-slab_typesafe_by_rcu.patch mm-slab-allow-freeptr_offset-to-be-used-with-ctor.patch docs-mm-document-latest-changes-to-vm_lock.patch