On Tue, Aug 6, 2024 at 4:08 AM Zhiguo Jiang <justinjiang@xxxxxxxx> wrote: > > Support mTHP's attempt to free swap entries as a whole, which can avoid > frequent swap_info locking for every individual entry in > swapcache_free_entries(). When the swap_map count values corresponding > to all contiguous entries are all zero excluding SWAP_HAS_CACHE, the > entries will be freed directly by skippping percpu swp_slots caches. > No, this isn't quite good. Please review the work done by Chris and Kairui[1]; they have handled it better. On a different note, I have a patch that can handle zap_pte_range() for swap entries in batches[2][3]. [1] https://lore.kernel.org/linux-mm/20240730-swap-allocator-v5-5-cb9c148b9297@xxxxxxxxxx/ [2] https://lore.kernel.org/linux-mm/20240803091118.84274-1-21cnbao@xxxxxxxxx/ [3] https://lore.kernel.org/linux-mm/CAGsJ_4wPnQqKOHx6iQcwO8bQzoBXKr2qY2AgSxMwTQCj3-8YWw@xxxxxxxxxxxxxx/ > Signed-off-by: Zhiguo Jiang <justinjiang@xxxxxxxx> > --- > mm/swapfile.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 61 insertions(+) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index ea023fc25d08..829fb4cfb6ec > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -1493,6 +1493,58 @@ static void swap_entry_range_free(struct swap_info_struct *p, swp_entry_t entry, > swap_range_free(p, offset, nr_pages); > } > > +/* > + * Free the contiguous swap entries as a whole, caller have to > + * ensure all entries belong to the same folio. > + */ > +static void swap_entry_range_check_and_free(struct swap_info_struct *p, > + swp_entry_t entry, int nr, bool *any_only_cache) > +{ > + const unsigned long start_offset = swp_offset(entry); > + const unsigned long end_offset = start_offset + nr; > + unsigned long offset; > + DECLARE_BITMAP(to_free, SWAPFILE_CLUSTER) = { 0 }; > + struct swap_cluster_info *ci; > + int i = 0, nr_setbits = 0; > + unsigned char count; > + > + /* > + * Free and check swap_map count values corresponding to all contiguous > + * entries in the whole folio range. > + */ > + WARN_ON_ONCE(nr > SWAPFILE_CLUSTER); > + ci = lock_cluster_or_swap_info(p, start_offset); > + for (offset = start_offset; offset < end_offset; offset++, i++) { > + if (data_race(p->swap_map[offset])) { > + count = __swap_entry_free_locked(p, offset, 1); > + if (!count) { > + bitmap_set(to_free, i, 1); > + nr_setbits++; > + } else if (count == SWAP_HAS_CACHE) { > + *any_only_cache = true; > + } > + } else { > + WARN_ON_ONCE(1); > + } > + } > + unlock_cluster_or_swap_info(p, ci); > + > + /* > + * If the swap_map count values corresponding to all contiguous entries are > + * all zero excluding SWAP_HAS_CACHE, the entries will be freed directly by > + * skippping percpu swp_slots caches, which can avoid frequent swap_info > + * locking for every individual entry. > + */ > + if (nr > 1 && nr_setbits == nr) { > + spin_lock(&p->lock); > + swap_entry_range_free(p, entry, nr); > + spin_unlock(&p->lock); > + } else { > + for_each_set_bit(i, to_free, SWAPFILE_CLUSTER) > + free_swap_slot(swp_entry(p->type, start_offset + i)); > + } > +} > + > static void cluster_swap_free_nr(struct swap_info_struct *sis, > unsigned long offset, int nr_pages, > unsigned char usage) > @@ -1808,6 +1860,14 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr) > if (WARN_ON(end_offset > si->max)) > goto out; > > + /* > + * Try to free all contiguous entries about mTHP as a whole. > + */ > + if (IS_ENABLED(CONFIG_THP_SWAP) && nr > 1) { > + swap_entry_range_check_and_free(si, entry, nr, &any_only_cache); > + goto free_cache; > + } > + > /* > * First free all entries in the range. > */ > @@ -1821,6 +1881,7 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr) > } > } > > +free_cache: > /* > * Short-circuit the below loop if none of the entries had their > * reference drop to zero. > -- > 2.39.0 >
