On 21/10/2024 22:11, Yosry Ahmed wrote: > 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? > I think the cost of tree lookup is not much and compared to zswap_decompress can probably be ignored. zswap_present_test is essentially just xa_load for the first entry, and then xas_next_entry for subsequent entries which is even cheaper than xa_load.
