From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 556F42EEE86 for ; Sat, 25 Jul 2026 09:40:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784972432; cv=none; b=PTsNf6SwX+L0X4S/fmQvrUqK99htI8MpScawUeJRiiPhyQJVQuXAKHc8Qtsn4bovmjm6cJwY/XgFBXsJ2H9dqN4FI+y3uIrO57Ea3ZH8hjdI6RwYPKLQ+8ox6y1wsY0Ow+1TqkieNriZxrN3JapE7JxhbwLG6iol/6XPU7iHjDg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784972432; c=relaxed/simple; bh=65XZfVffm0RKIEz/C/W4KYgIhSA+aKRV1kbxBpLGH2U=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rV4fZgWrED0m30s5aYbbFzEwHX2l8uNENlS5HC3qCvFgnErDkVtAKy7NJTMgnQVCiYVzMYJYghA86lhRKL7G675PH+t+WbegEZEtP7w4n2l9VV8fK1uRbhm+sO4X7m83PADOeTiwIar0bEoYRhD5tGvvYsrGvo2XObU+yitLAG8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=YFWn/ySZ; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="YFWn/ySZ" 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 C2C051476; Sat, 25 Jul 2026 02:40:23 -0700 (PDT) Received: from [10.164.11.99] (unknown [10.164.11.99]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 354C13F86F; Sat, 25 Jul 2026 02:40:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1784972427; bh=65XZfVffm0RKIEz/C/W4KYgIhSA+aKRV1kbxBpLGH2U=; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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