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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=YFWn/ySZO34odXGS/hZ1LontckFFcbvMpjRBnIwfDoI3NeZWo2FNmR+tpF9Y7a/XA nEfYNUG/lkdpGiI5wlQcit1T5EekH56T8vxmT7HQb/7eNX1yJz3+Cd2EKmiFW9A9OT PCj9HcbMc/0P0H4HpZCdWWUkRJCupOSFRj4yo3A4= Message-ID: Date: Sat, 25 Jul 2026 15:10:18 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/8] mm/swapfile: add batched version of folio_put_swap To: Barry Song Cc: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, baoquan.he@linux.dev, youngjun.park@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, pfalcato@suse.de, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20260723070905.3422276-1-dev.jain@arm.com> <20260723070905.3422276-3-dev.jain@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 6F26320005 X-Stat-Signature: h6g3cbm6mwgfesmg19erxu6riegujohn X-Rspam-User: X-HE-Tag: 1784972429-75933 X-HE-Meta: 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 EEb+61+D DKvsmPjNGX/czuG2P1lvwnL8T/1aG4JKOVBFcljtlBvU1afVVZ6GJwBDzh+8TcwHHqman0fQ+ZQdl0etBrv6c6x2bVWzU8KTIRIII5lHBqcOEFgUZt6umGzquBAAWH3dpNMfN+ZlUdThzG3oPNdZRhMNJzEf+ZDSbLWa3aqHTvJbz9e/ls9puKePc8lf/CsoqM09SGFT5hsTwrtcUIvL+QF1ER6WvRZyggQAzCt0+9+UeDsA/fPLIGrv/rXYxkMuup8c48055FxfBeS8aXRWOc4lM4XCuomlQPSvOnve7GdzNcq9sBaIKDWQUexTh4S3e23JKVOgcOldG+V7X9W0N52OnlldfQaizAMws+rAtpVBPSgTvwHZ7MHQOHDNZ4vHY/cKNNdLAXbim5ok= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 25/07/26 10:23 am, Barry Song wrote: > On Thu, Jul 23, 2026 at 3:09 PM Dev Jain wrote: >> >> Add folio_put_swap_pages to handle a batch of consecutive pages. Note >> that folio_put_swap already can handle a subset of this: nr_pages == 1 and >> nr_pages == folio_nr_pages(folio). Generalize this to any nr_pages. >> >> Currently we have a not-so-nice logic of passing in subpage == NULL if >> we mean to exercise the logic on the entire folio, and subpage != NULL if >> we want to exercise the logic on only that subpage. Remove this >> indirection: the caller invokes folio_put_swap_pages() if it wants to >> operate on a range of pages in the folio (i.e nr_pages may be anything >> between 1 and folio_nr_pages()), and invokes folio_put_swap() if it >> wants to operate on the entire folio. >> >> Acked-by: David Hildenbrand (Arm) >> Signed-off-by: Dev Jain > > Reviewed-by: Barry Song Thanks for your review. > > [...] >> >> diff --git a/mm/memory.c b/mm/memory.c >> index a620d425ec95e..d88df15018268 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -5198,7 +5198,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >> if (unlikely(folio != swapcache)) { >> folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSIVE); >> folio_add_lru_vma(folio, vma); >> - folio_put_swap(swapcache, NULL); >> + folio_put_swap(swapcache); >> } else if (!folio_test_anon(folio)) { >> /* >> * We currently only expect !anon folios that are fully >> @@ -5207,12 +5207,12 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >> VM_WARN_ON_ONCE_FOLIO(folio_nr_pages(folio) != nr_pages, folio); >> VM_WARN_ON_ONCE_FOLIO(folio_mapped(folio), folio); >> folio_add_new_anon_rmap(folio, vma, address, rmap_flags); >> - folio_put_swap(folio, NULL); >> + folio_put_swap(folio); >> } else { >> VM_WARN_ON_ONCE(nr_pages != 1 && nr_pages != folio_nr_pages(folio)); >> folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, address, >> rmap_flags); >> - folio_put_swap(folio, nr_pages == 1 ? page : NULL); >> + folio_put_swap_pages(folio, page, nr_pages); > > Yes. In do_swap_page(), `page` points to the first page of the > large folio. > if (folio_test_large(folio) && folio_test_swapcache(folio)) { > ... > page = &folio->page; > } > >> --- a/mm/swapfile.c >> +++ b/mm/swapfile.c >> @@ -1817,27 +1817,25 @@ int folio_dup_swap_pages(struct folio *folio, struct page *page, >> } >> >> /** >> - * folio_put_swap() - Decrease swap count of swap entries of a folio. >> + * folio_put_swap_pages() - Decrease swap count of swap entries of a folio. >> * @folio: folio with swap entries bounded, must be in swap cache and locked. >> - * @page: if not NULL, only decrease the swap count of this page. >> + * @page: the first page in the folio to decrease the swap count for. >> + * @nr_pages: the number of pages in the folio to decrease the swap count for. >> * >> * This won't free the swap slots even if swap count drops to zero, they are >> * still pinned by the swap cache. User may call folio_free_swap to free them. >> * Context: Caller must ensure the folio is locked and in the swap cache. >> */ >> -void folio_put_swap(struct folio *folio, struct page *page) >> +void folio_put_swap_pages(struct folio *folio, struct page *page, >> + unsigned long nr_pages) >> { >> swp_entry_t entry = folio->swap; >> - unsigned long nr_pages = folio_nr_pages(folio); >> struct swap_info_struct *si = __swap_entry_to_info(entry); >> >> VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); >> VM_WARN_ON_FOLIO(!folio_test_swapcache(folio), folio); >> >> - if (page) { >> - entry.val += folio_page_idx(folio, page); >> - nr_pages = 1; >> - } >> + entry.val += folio_page_idx(folio, page); >> >> swap_put_entries_cluster(si, swp_offset(entry), nr_pages, false); > > Maybe a guard against potential overflow would help? also in patch 1? > > idx = folio_page_idx(folio, page); > > VM_WARN_ON_FOLIO(idx + nr_pages > folio_nr_pages(folio), folio); We had this discussion before and I am struggling to recall that - I think there are currently both cases, the batched helpers not doing the sanity checking but documenting it (I haven't documented it in this one, and in set_softleaf_ptes too, will audit later), or doing the sanity checking. But I also recall the expectation is that CONFIG_DEBUG_VM is not used in production kernels, so I can put this in v2. > > Best Regards > Barry