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 420001A6812 for ; Wed, 11 Mar 2026 05:42:33 +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=1773207754; cv=none; b=I/ZjxAZUGZgBhuCEwZGNz7PAEZz9saHzf1BpA96JLWF32tAHKzgj3exq0bFqdFMgdV75XDkcb1+Iz57wLtWQimxUF9lsi7jQ9eEnn8qnIpbSdOz0sYI1POumfaP6rx6//16Itc/+uv8++AtG8dOJicmQ6jlK1nmUC15OJD19p3Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773207754; c=relaxed/simple; bh=wZA+LaBAoxQof7UhprmEar53+eFLkttQun1MxSYseDc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IZfD6r4iS5iI2KdpZTG/lZrWAiMs71mNJwXn8L9Vt2paCmoRrnMcQmAbtLl5sAD7v6bTtTCEv7ExOoqpxZROqXoDOK+paeaTudvKV7k7LnhQeRZJXj0Jii9sHfykFP3kBAjC4Icb0fEvVVqyYwxptBf4ZvJCKhi5j01t3Uj2Lc0= 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; 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 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 77595165C; Tue, 10 Mar 2026 22:42:26 -0700 (PDT) Received: from [10.164.19.59] (unknown [10.164.19.59]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DB7473F7BD; Tue, 10 Mar 2026 22:42:24 -0700 (PDT) Message-ID: <26631dbf-1a3e-4d30-9a07-ff64319cbf2f@arm.com> Date: Wed, 11 Mar 2026 11:12:22 +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 6/9] mm/swapfile: Make folio_dup_swap batchable To: "Lorenzo Stoakes (Oracle)" Cc: akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, david@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com, weixugc@google.com, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, pfalcato@suse.de, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, baohua@kernel.org, youngjun.park@lge.com, ziy@nvidia.com, kas@kernel.org, willy@infradead.org, yuzhao@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20260310073013.4069309-1-dev.jain@arm.com> <20260310073013.4069309-7-dev.jain@arm.com> <18928285-20c6-4cd9-842f-c0aef91421a2@lucifer.local> Content-Language: en-US From: Dev Jain In-Reply-To: <18928285-20c6-4cd9-842f-c0aef91421a2@lucifer.local> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/03/26 2:19 pm, Lorenzo Stoakes (Oracle) wrote: > On Tue, Mar 10, 2026 at 01:00:10PM +0530, Dev Jain wrote: >> Teach folio_dup_swap to handle a batch of consecutive pages. Note that >> folio_dup_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, and explicitly pass subpage != NULL, and the number of >> pages required. > > You've made the interface more confusing? Now we can update multiple subpages > but specify only one? :) > > Let's try to actually refactor this into something sane... see below. > >> >> Signed-off-by: Dev Jain >> --- >> mm/rmap.c | 2 +- >> mm/shmem.c | 2 +- >> mm/swap.h | 5 +++-- >> mm/swapfile.c | 12 +++++------- >> 4 files changed, 10 insertions(+), 11 deletions(-) >> >> diff --git a/mm/rmap.c b/mm/rmap.c >> index dd638429c963e..f6d5b187cf09b 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -2282,7 +2282,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >> goto discard; >> } >> >> - if (folio_dup_swap(folio, subpage) < 0) { >> + if (folio_dup_swap(folio, subpage, 1) < 0) { >> set_pte_at(mm, address, pvmw.pte, pteval); >> goto walk_abort; >> } >> diff --git a/mm/shmem.c b/mm/shmem.c >> index 5e7dcf5bc5d3c..86ee34c9b40b3 100644 >> --- a/mm/shmem.c >> +++ b/mm/shmem.c >> @@ -1695,7 +1695,7 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug, >> spin_unlock(&shmem_swaplist_lock); >> } >> >> - folio_dup_swap(folio, NULL); >> + folio_dup_swap(folio, folio_page(folio, 0), folio_nr_pages(folio)); >> shmem_delete_from_page_cache(folio, swp_to_radix_entry(folio->swap)); >> >> BUG_ON(folio_mapped(folio)); >> diff --git a/mm/swap.h b/mm/swap.h >> index a77016f2423b9..d9cb58ebbddd1 100644 >> --- a/mm/swap.h >> +++ b/mm/swap.h >> @@ -206,7 +206,7 @@ extern int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp); >> * folio_put_swap(): does the opposite thing of folio_dup_swap(). >> */ >> int folio_alloc_swap(struct folio *folio); >> -int folio_dup_swap(struct folio *folio, struct page *subpage); >> +int folio_dup_swap(struct folio *folio, struct page *subpage, unsigned int nr_pages); >> void folio_put_swap(struct folio *folio, struct page *subpage); >> >> /* For internal use */ >> @@ -390,7 +390,8 @@ static inline int folio_alloc_swap(struct folio *folio) >> return -EINVAL; >> } >> >> -static inline int folio_dup_swap(struct folio *folio, struct page *page) >> +static inline int folio_dup_swap(struct folio *folio, struct page *page, >> + unsigned int nr_pages) >> { >> return -EINVAL; >> } >> diff --git a/mm/swapfile.c b/mm/swapfile.c >> index 915bc93964dbd..eaf61ae6c3817 100644 >> --- a/mm/swapfile.c >> +++ b/mm/swapfile.c >> @@ -1738,7 +1738,8 @@ int folio_alloc_swap(struct folio *folio) >> /** >> * folio_dup_swap() - Increase swap count of swap entries of a folio. >> * @folio: folio with swap entries bounded. >> - * @subpage: if not NULL, only increase the swap count of this subpage. >> + * @subpage: Increase the swap count of this subpage till nr number of >> + * pages forward. > > (Obviously also Kairui's point about missing entry in kdoc) > > This is REALLY confusing sorry. And this interface is just a horror show. > > Before we had subpage == only increase the swap count of the subpage. > > Now subpage = the first subpage at which we do that? Please, no. > > You just need to rework this interface in general, this is a hack. > > Something like: > > int __folio_dup_swap(struct folio *folio, unsigned int subpage_start_index, > unsigned int nr_subpages) > { > ... > } > > ... > > int folio_dup_swap_subpage(struct folio *folio, struct page *subpage) > { > return __folio_dup_swap(folio, folio_page_idx(folio, subpage), 1); > } > > int folio_dup_swap(struct folio *folio) > { > return __folio_dup_swap(folio, 0, folio_nr_pages(folio)); > } > > Or something like that. I get the essence of the point you are making. Since most callers of folio_put_swap mean it for entire folio, perhaps we can have folio_put_swap for these callers, and the ones which are not sure can call folio_put_swap_subpages? Same for folio_dup_swap. And since we are calling it folio_put_swap_subpages, we can retain the subpage parameter? > > We're definitely _not_ keeping the subpage parameter like that and hacking on > batching, PLEASE. > >> * >> * Typically called when the folio is unmapped and have its swap entry to >> * take its place: Swap entries allocated to a folio has count == 0 and pinned >> @@ -1752,18 +1753,15 @@ int folio_alloc_swap(struct folio *folio) >> * swap_put_entries_direct on its swap entry before this helper returns, or >> * the swap count may underflow. >> */ >> -int folio_dup_swap(struct folio *folio, struct page *subpage) >> +int folio_dup_swap(struct folio *folio, struct page *subpage, >> + unsigned int nr_pages) >> { >> swp_entry_t entry = folio->swap; >> - unsigned long nr_pages = folio_nr_pages(folio); >> >> VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); >> VM_WARN_ON_FOLIO(!folio_test_swapcache(folio), folio); >> >> - if (subpage) { >> - entry.val += folio_page_idx(folio, subpage); >> - nr_pages = 1; >> - } >> + entry.val += folio_page_idx(folio, subpage); >> >> return swap_dup_entries_cluster(swap_entry_to_info(entry), >> swp_offset(entry), nr_pages); >> -- >> 2.34.1 >> > > Thanks, Lorenzo