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Tue, 08 Apr 2025 22:24:59 -0400 X-MC-Unique: 2UVoF_rkM--J4w6KkhOSBw-1 X-Mimecast-MFC-AGG-ID: 2UVoF_rkM--J4w6KkhOSBw_1744165498 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CDEDD180049D; Wed, 9 Apr 2025 02:24:57 +0000 (UTC) Received: from localhost (unknown [10.72.112.61]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 15C963001D0E; Wed, 9 Apr 2025 02:24:55 +0000 (UTC) Date: Wed, 9 Apr 2025 10:24:51 +0800 From: Baoquan He To: Andrew Morton , Kemeng Shi Cc: kernel test robot , llvm@lists.linux.dev, oe-kbuild-all@lists.linux.dev, Linux Memory Management List , Tim Chen Subject: Re: [linux-next:master 1753/1936] mm/swapfile.c:1517:20: warning: function 'swap_is_last_ref' is not needed and will not be emitted Message-ID: References: <202504081841.jbL7yL0r-lkp@intel.com> <20250408173959.f501f65ec5d5e52cefe6b129@linux-foundation.org> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20250408173959.f501f65ec5d5e52cefe6b129@linux-foundation.org> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 2c_sFSKki68lj7Tze3DAhne3V_8JrXOCWdZlD-KRpBo_1744165498 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On 04/08/25 at 05:39pm, Andrew Morton wrote: > On Tue, 8 Apr 2025 18:06:11 +0800 kernel test robot wrote: > > > tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master > > head: 7702d0130dc002bab2c3571ddb6ff68f82d99aea > > commit: 6bb001b6b64ec20d900d0d81294a0f031af59c3e [1753/1936] mm: swap: enable swap_entry_range_free() to drop any kind of last ref > > config: hexagon-randconfig-001-20250408 (https://download.01.org/0day-ci/archive/20250408/202504081841.jbL7yL0r-lkp@intel.com/config) > > compiler: clang version 21.0.0git (https://github.com/llvm/llvm-project 92c93f5286b9ff33f27ff694d2dc33da1c07afdd) > > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250408/202504081841.jbL7yL0r-lkp@intel.com/reproduce) > > > > If you fix the issue in a separate patch/commit (i.e. not just a new version of > > the same patch/commit), kindly add following tags > > | Reported-by: kernel test robot > > | Closes: https://lore.kernel.org/oe-kbuild-all/202504081841.jbL7yL0r-lkp@intel.com/ > > > > All warnings (new ones prefixed by >>): > > > > >> mm/swapfile.c:1517:20: warning: function 'swap_is_last_ref' is not needed and will not be emitted [-Wunneeded-internal-declaration] > > It's annoying that gcc warns about this. > > > 1517 | static inline bool swap_is_last_ref(unsigned char count) > > | ^~~~~~~~~~~~~~~~ > > 1 warning generated. > > > > > > vim +/swap_is_last_ref +1517 mm/swapfile.c > > > > 1512 > > 1513 /* > > 1514 * Drop the last ref(1, SWAP_HAS_CACHE or SWAP_MAP_SHMEM) of swap entries, > > 1515 * caller have to ensure all entries belong to the same cgroup and cluster. > > 1516 */ > > > 1517 static inline bool swap_is_last_ref(unsigned char count) > > 1518 { > > 1519 return (count == SWAP_HAS_CACHE) || (count == 1) || > > 1520 (count == SWAP_MAP_SHMEM); > > 1521 } > > 1522 > > : static inline bool swap_is_last_ref(unsigned char count) > : { > : return (count == SWAP_HAS_CACHE) || (count == 1) || > : (count == SWAP_MAP_SHMEM); > : } > : > : static void swap_entries_free(struct swap_info_struct *si, > : struct swap_cluster_info *ci, > : swp_entry_t entry, unsigned int nr_pages) > : { > : unsigned long offset = swp_offset(entry); > : unsigned char *map = si->swap_map + offset; > : unsigned char *map_end = map + nr_pages; > : > : /* It should never free entries across different clusters */ > : VM_BUG_ON(ci != offset_to_cluster(si, offset + nr_pages - 1)); > : VM_BUG_ON(cluster_is_empty(ci)); > : VM_BUG_ON(ci->count < nr_pages); > : > : ci->count -= nr_pages; > : do { > : VM_BUG_ON(!swap_is_last_ref(*map)); > > > And it's annoying that VM_BUG_ON() doesn't reference its arg when > CONFIG_DEBUG_VM=n. > > I'll add this: > > --- a/mm/swapfile.c~mm-swap-enable-swap_entry_range_free-to-drop-any-kind-of-last-ref-fix > +++ a/mm/swapfile.c > @@ -1514,11 +1514,13 @@ fallback: > * Drop the last ref(1, SWAP_HAS_CACHE or SWAP_MAP_SHMEM) of swap entries, > * caller have to ensure all entries belong to the same cgroup and cluster. > */ > +#ifdef CONFIG_DEBUG_VM > static inline bool swap_is_last_ref(unsigned char count) > { > return (count == SWAP_HAS_CACHE) || (count == 1) || > (count == SWAP_MAP_SHMEM); > } > +#endif > > static void swap_entries_free(struct swap_info_struct *si, > struct swap_cluster_info *ci, > _ > > Kemeng, can you please review that comment "Drop the last ref...". > From its positioning it appears to be describing swap_is_last_ref(), > but swap_is_last_ref() doesn't do those things. Indeed, maybe below change can be squashed into above patch from Andrew. diff --git a/mm/swapfile.c b/mm/swapfile.c index 2887ed5d34cc..baaf8ad29a6b 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1536,8 +1536,8 @@ static bool swap_entries_put_map_nr(struct swap_info_struct *si, } /* - * Drop the last ref(1, SWAP_HAS_CACHE or SWAP_MAP_SHMEM) of swap entries, - * caller have to ensure all entries belong to the same cgroup and cluster. + * Check if it's the last ref of swap entry in the freeing path. + * Qualified vlaue includes 1, SWAP_HAS_CACHE or SWAP_MAP_SHMEM. */ static inline bool swap_is_last_ref(unsigned char count) {