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([2a02:6b67:d751:7400:c2b:f323:d172:e42a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4316f5c311bsm95896925e9.29.2024.10.22.12.59.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Oct 2024 12:59:56 -0700 (PDT) Message-ID: <032b5d28-68bb-4fea-91f7-e4a8bc4c4bb6@gmail.com> Date: Tue, 22 Oct 2024 20:59:55 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 1/4] mm/zswap: skip swapcache for swapping in zswap pages To: Yosry Ahmed Cc: akpm@linux-foundation.org, linux-mm@kvack.org, hannes@cmpxchg.org, david@redhat.com, willy@infradead.org, kanchana.p.sridhar@intel.com, nphamcs@gmail.com, chengming.zhou@linux.dev, ryan.roberts@arm.com, ying.huang@intel.com, 21cnbao@gmail.com, riel@surriel.com, shakeel.butt@linux.dev, kernel-team@meta.com, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org References: <20241018105026.2521366-1-usamaarif642@gmail.com> <20241018105026.2521366-2-usamaarif642@gmail.com> Content-Language: en-US From: Usama Arif In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 8604A1C0036 X-Stat-Signature: nhphymt3n1mddu16x4utzn3hqanekofq X-Rspam-User: X-HE-Tag: 1729627191-157584 X-HE-Meta: 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 GhutvhhF 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 21/10/2024 22:11, Yosry Ahmed wrote: > On Fri, Oct 18, 2024 at 3:50 AM Usama Arif 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@kernel.org/T/#m5a792a04dfea20eb7af4c355d00503efe1c86a93 >> >> Signed-off-by: Usama Arif >> --- >> 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.