On Fri, Oct 18, 2024 at 3:50 AM Usama Arif <usamaarif642@xxxxxxxxx> wrote: > > As mentioned in [1], there is a significant improvement in no > readahead swapin performance for super fast devices when skipping > swapcache. > > With large folio zswapin support added in later patches, this will also > mean this path will also act as "readahead" by swapping in multiple > pages into large folios. further improving performance. > > [1] https://lore.kernel.org/all/1505886205-9671-5-git-send-email-minchan@xxxxxxxxxx/T/#m5a792a04dfea20eb7af4c355d00503efe1c86a93 > > Signed-off-by: Usama Arif <usamaarif642@xxxxxxxxx> > --- > include/linux/zswap.h | 6 ++++++ > mm/memory.c | 3 ++- > mm/page_io.c | 1 - > mm/zswap.c | 46 +++++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 54 insertions(+), 2 deletions(-) > > diff --git a/include/linux/zswap.h b/include/linux/zswap.h > index d961ead91bf1..e418d75db738 100644 > --- a/include/linux/zswap.h > +++ b/include/linux/zswap.h > @@ -27,6 +27,7 @@ struct zswap_lruvec_state { > unsigned long zswap_total_pages(void); > bool zswap_store(struct folio *folio); > bool zswap_load(struct folio *folio); > +bool zswap_present_test(swp_entry_t swp, int nr_pages); > void zswap_invalidate(swp_entry_t swp); > int zswap_swapon(int type, unsigned long nr_pages); > void zswap_swapoff(int type); > @@ -49,6 +50,11 @@ static inline bool zswap_load(struct folio *folio) > return false; > } > > +static inline bool zswap_present_test(swp_entry_t swp, int nr_pages) > +{ > + return false; > +} > + > static inline void zswap_invalidate(swp_entry_t swp) {} > static inline int zswap_swapon(int type, unsigned long nr_pages) > { > diff --git a/mm/memory.c b/mm/memory.c > index 03e5452dd0c0..49d243131169 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4289,7 +4289,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > swapcache = folio; > > if (!folio) { > - if (data_race(si->flags & SWP_SYNCHRONOUS_IO) && > + if ((data_race(si->flags & SWP_SYNCHRONOUS_IO) || > + zswap_present_test(entry, 1)) && > __swap_count(entry) == 1) { > /* skip swapcache */ > folio = alloc_swap_folio(vmf); > diff --git a/mm/page_io.c b/mm/page_io.c > index 4aa34862676f..2a15b197968a 100644 > --- a/mm/page_io.c > +++ b/mm/page_io.c > @@ -602,7 +602,6 @@ void swap_read_folio(struct folio *folio, struct swap_iocb **plug) > unsigned long pflags; > bool in_thrashing; > > - VM_BUG_ON_FOLIO(!folio_test_swapcache(folio) && !synchronous, folio); > VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); > VM_BUG_ON_FOLIO(folio_test_uptodate(folio), folio); > > diff --git a/mm/zswap.c b/mm/zswap.c > index 7f00cc918e7c..f4b03071b2fb 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -1576,6 +1576,52 @@ bool zswap_store(struct folio *folio) > return ret; > } > > +static bool swp_offset_in_zswap(unsigned int type, pgoff_t offset) > +{ > + return (offset >> SWAP_ADDRESS_SPACE_SHIFT) < nr_zswap_trees[type]; > +} > + > +/* Returns true if the entire folio is in zswap */ > +bool zswap_present_test(swp_entry_t swp, int nr_pages) Also, did you check how the performance changes if we bring back the bitmap of present entries (i.e. what used to be frontswap's bitmap) instead of the tree lookups here? > +{ > + pgoff_t offset = swp_offset(swp), tree_max_idx; > + int max_idx = 0, i = 0, tree_offset = 0; > + unsigned int type = swp_type(swp); > + struct zswap_entry *entry = NULL; > + struct xarray *tree; > + > + while (i < nr_pages) { > + tree_offset = offset + i; > + /* Check if the tree exists. */ > + if (!swp_offset_in_zswap(type, tree_offset)) > + return false; > + > + tree = swap_zswap_tree(swp_entry(type, tree_offset)); > + XA_STATE(xas, tree, tree_offset); > + > + tree_max_idx = tree_offset % SWAP_ADDRESS_SPACE_PAGES ? > + ALIGN(tree_offset, SWAP_ADDRESS_SPACE_PAGES) : > + ALIGN(tree_offset + 1, SWAP_ADDRESS_SPACE_PAGES); > + max_idx = min(offset + nr_pages, tree_max_idx) - 1; > + rcu_read_lock(); > + xas_for_each(&xas, entry, max_idx) { > + if (xas_retry(&xas, entry)) > + continue; > + i++; > + } > + rcu_read_unlock(); > + /* > + * If xas_for_each exits because entry is NULL and > + * the number of entries checked are less then max idx, > + * then zswap does not contain the entire folio. > + */ > + if (!entry && offset + i <= max_idx) > + return false; > + } > + > + return true; > +} > + > bool zswap_load(struct folio *folio) > { > swp_entry_t swp = folio->swap; > -- > 2.43.5 >
