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imf27.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf27.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1712921308; a=rsa-sha256; cv=none; b=b4k2RFOlor6FWLIkKsdEo9+maFpUHG597OVJ+tNaA113WxV8QDJ9+GmX64kOk3tMdoyEtq QmZME3ewXlNz7nB45JRomAu+gcRKj9mz/Mqw0hAJkOdNYows7xZTQToQIppKXIHPrjtACy hz1aKCUFW0yEd9OlnVT4aDNTaG1RWyM= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C208D339; Fri, 12 Apr 2024 04:28:56 -0700 (PDT) Received: from [10.57.73.208] (unknown [10.57.73.208]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DA6D73F766; Fri, 12 Apr 2024 04:28:24 -0700 (PDT) Message-ID: <66afc978-0221-488b-9fc6-7d5213d385ed@arm.com> Date: Fri, 12 Apr 2024 12:28:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/5] mm: swap: introduce swap_free_nr() for batched swap_free() Content-Language: en-GB To: Chuanhua Han Cc: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, hanchuanhua@oppo.com, hannes@cmpxchg.org, hughd@google.com, kasong@tencent.com, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, xiang@kernel.org, ying.huang@intel.com, yosryahmed@google.com, yuzhao@google.com, ziy@nvidia.com, linux-kernel@vger.kernel.org References: <20240409082631.187483-1-21cnbao@gmail.com> <20240409082631.187483-2-21cnbao@gmail.com> <95bc0ebb-49f4-4331-8809-3e4625f1d91a@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: zec7s9wpcxa4i3taf9ek35t7quawggig X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 621B84000A X-HE-Tag: 1712921308-804269 X-HE-Meta: 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 PaJb1CJ9 d7/mB+M2WBDcicdXtA35mPduRBlzEmQqtnDk7JxdPsiM2CfzufdvbkUQ+pb0OgrCww7Ugv2vu87TDkP6jcmqDQuPapka+Lj+95yghOIAK9ipMB8REc5rJSQwz+cpq1M/qJNRhJrC0fYsKqzX5FpmTHZLp2b7VuJyD76I51w4PfuHd3Zoy030/nkHeBSaHy1m0x78Bs2Wym+FMaSkD44NMLtjv9beh4ECxpBip5T8Y60FZDMBdNh4Y9JC0s8ORn29ZjNCBPGk9QYKryBE2l5GGGEQqv3eW/Fk5MpLwoZGe///o9ce1QcZZDWv3OZqC2tEG4YqXzrb4wTjJr9ZVjLAOWo823w== 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 12/04/2024 03:07, Chuanhua Han wrote: > Ryan Roberts 于2024年4月11日周四 22:30写道： >> >> On 09/04/2024 09:26, Barry Song wrote: >>> From: Chuanhua Han >>> >>> While swapping in a large folio, we need to free swaps related to the whole >>> folio. To avoid frequently acquiring and releasing swap locks, it is better >>> to introduce an API for batched free. >>> >>> Signed-off-by: Chuanhua Han >>> Co-developed-by: Barry Song >>> Signed-off-by: Barry Song >> >> Couple of nits; feel free to ignore. >> >> Reviewed-by: Ryan Roberts >> >>> --- >>> include/linux/swap.h | 5 +++++ >>> mm/swapfile.c | 51 ++++++++++++++++++++++++++++++++++++++++++++ >>> 2 files changed, 56 insertions(+) >>> >>> diff --git a/include/linux/swap.h b/include/linux/swap.h >>> index 11c53692f65f..b7a107e983b8 100644 >>> --- a/include/linux/swap.h >>> +++ b/include/linux/swap.h >>> @@ -483,6 +483,7 @@ extern void swap_shmem_alloc(swp_entry_t); >>> extern int swap_duplicate(swp_entry_t); >>> extern int swapcache_prepare(swp_entry_t); >>> extern void swap_free(swp_entry_t); >>> +extern void swap_free_nr(swp_entry_t entry, int nr_pages); >>> extern void swapcache_free_entries(swp_entry_t *entries, int n); >>> extern void free_swap_and_cache_nr(swp_entry_t entry, int nr); >>> int swap_type_of(dev_t device, sector_t offset); >>> @@ -564,6 +565,10 @@ static inline void swap_free(swp_entry_t swp) >>> { >>> } >>> >>> +void swap_free_nr(swp_entry_t entry, int nr_pages) >>> +{ >>> +} >>> + >>> static inline void put_swap_folio(struct folio *folio, swp_entry_t swp) >>> { >>> } >>> diff --git a/mm/swapfile.c b/mm/swapfile.c >>> index 28642c188c93..f4c65aeb088d 100644 >>> --- a/mm/swapfile.c >>> +++ b/mm/swapfile.c >>> @@ -1356,6 +1356,57 @@ void swap_free(swp_entry_t entry) >>> __swap_entry_free(p, entry); >>> } >>> >>> +/* >>> + * Free up the maximum number of swap entries at once to limit the >>> + * maximum kernel stack usage. >>> + */ >>> +#define SWAP_BATCH_NR (SWAPFILE_CLUSTER > 512 ? 512 : SWAPFILE_CLUSTER) >>> + >>> +/* >>> + * Called after swapping in a large folio, batched free swap entries >>> + * for this large folio, entry should be for the first subpage and >>> + * its offset is aligned with nr_pages >>> + */ >>> +void swap_free_nr(swp_entry_t entry, int nr_pages) >>> +{ >>> + int i, j; >>> + struct swap_cluster_info *ci; >>> + struct swap_info_struct *p; >>> + unsigned int type = swp_type(entry); >>> + unsigned long offset = swp_offset(entry); >>> + int batch_nr, remain_nr; >>> + DECLARE_BITMAP(usage, SWAP_BATCH_NR) = { 0 }; >>> + >>> + /* all swap entries are within a cluster for mTHP */ >>> + VM_BUG_ON(offset % SWAPFILE_CLUSTER + nr_pages > SWAPFILE_CLUSTER); >>> + >>> + if (nr_pages == 1) { >>> + swap_free(entry); >>> + return; >>> + } >>> + >>> + remain_nr = nr_pages; >>> + p = _swap_info_get(entry); >>> + if (p) { >> >> nit: perhaps return early if (!p) ? Then you dedent the for() block. > > Agreed! > >> >>> + for (i = 0; i < nr_pages; i += batch_nr) { >>> + batch_nr = min_t(int, SWAP_BATCH_NR, remain_nr); >>> + >>> + ci = lock_cluster_or_swap_info(p, offset); >>> + for (j = 0; j < batch_nr; j++) { >>> + if (__swap_entry_free_locked(p, offset + i * SWAP_BATCH_NR + j, 1)) >>> + __bitmap_set(usage, j, 1); >>> + } >>> + unlock_cluster_or_swap_info(p, ci); >>> + >>> + for_each_clear_bit(j, usage, batch_nr) >>> + free_swap_slot(swp_entry(type, offset + i * SWAP_BATCH_NR + j)); >>> + >> >> nit: perhaps change to for (;;), and do the checks here to avoid clearing the >> bitmap on the last run: >> >> i += batch_nr; >> if (i < nr_pages) >> break; > Great, thank you for your advice! Or maybe leave the for() as is, but don't explicitly init the bitmap at the start of the function and instead call: bitmap_clear(usage, 0, SWAP_BATCH_NR); At the start of each loop? >> >>> + bitmap_clear(usage, 0, SWAP_BATCH_NR); >>> + remain_nr -= batch_nr; >>> + } >>> + } >>> +} >>> + >>> /* >>> * Called after dropping swapcache to decrease refcnt to swap entries. >>> */ >> >> > >