Yosry Ahmed <yosryahmed@xxxxxxxxxx> writes: > In swap_range_free(), we update inuse_pages then do some cleanups (arch > invalidation, zswap invalidation, swap cache cleanups, etc). During > swapoff, try_to_unuse() uses inuse_pages to make sure all swap entries > are freed. Make sure we only update inuse_pages after we are done with > the cleanups. > > In practice, this shouldn't matter, because swap_range_free() is called > with the swap info lock held, and the swapoff code will spin for that > lock after try_to_unuse() anyway. > > The goal is to make it obvious and more future proof that once > try_to_unuse() returns, all cleanups are done. Defines "all cleanups". Apparently, some other operations are still to be done after try_to_unuse() in swap_off(). > This also facilitates a > following zswap cleanup patch which uses this fact to simplify > zswap_swapoff(). > > Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > --- > mm/swapfile.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 556ff7347d5f0..2fedb148b9404 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -737,8 +737,6 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset, > if (was_full && (si->flags & SWP_WRITEOK)) > add_to_avail_list(si); > } > - atomic_long_add(nr_entries, &nr_swap_pages); > - WRITE_ONCE(si->inuse_pages, si->inuse_pages - nr_entries); > if (si->flags & SWP_BLKDEV) > swap_slot_free_notify = > si->bdev->bd_disk->fops->swap_slot_free_notify; > @@ -752,6 +750,8 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset, > offset++; > } > clear_shadow_from_swap_cache(si->type, begin, end); > + atomic_long_add(nr_entries, &nr_swap_pages); > + WRITE_ONCE(si->inuse_pages, si->inuse_pages - nr_entries); This isn't enough. You need to use smp_wmb() here and smp_rmb() in somewhere reading si->inuse_pages. > } > > static void set_cluster_next(struct swap_info_struct *si, unsigned long next) -- Best Regards, Huang, Ying
