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Wed, 18 Mar 2026 15:30:23 -0700 (PDT) Received: from localhost ([2a03:2880:10ff:41::]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-41bd2d4cb20sm3817722fac.17.2026.03.18.15.30.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Mar 2026 15:30:22 -0700 (PDT) From: Nhat Pham To: kasong@tencent.com Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, apopple@nvidia.com, axelrasmussen@google.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, bhe@redhat.com, byungchul@sk.com, cgroups@vger.kernel.org, chengming.zhou@linux.dev, chrisl@kernel.org, corbet@lwn.net, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jannh@google.com, joshua.hahnjy@gmail.com, lance.yang@linux.dev, lenb@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pm@vger.kernel.org, lorenzo.stoakes@oracle.com, matthew.brost@intel.com, mhocko@suse.com, muchun.song@linux.dev, npache@redhat.com, nphamcs@gmail.com, pavel@kernel.org, peterx@redhat.com, peterz@infradead.org, pfalcato@suse.de, rafael@kernel.org, rakie.kim@sk.com, roman.gushchin@linux.dev, rppt@kernel.org, ryan.roberts@arm.com, shakeel.butt@linux.dev, shikemeng@huaweicloud.com, surenb@google.com, tglx@kernel.org, vbabka@suse.cz, weixugc@google.com, ying.huang@linux.alibaba.com, yosry.ahmed@linux.dev, yuanchu@google.com, zhengqi.arch@bytedance.com, ziy@nvidia.com, kernel-team@meta.com, riel@surriel.com Subject: [PATCH v4 17/21] swapfile: remove zeromap bitmap Date: Wed, 18 Mar 2026 15:29:48 -0700 Message-ID: <20260318222953.441758-18-nphamcs@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260318222953.441758-1-nphamcs@gmail.com> References: <20260318222953.441758-1-nphamcs@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 727D2C0008 X-Rspamd-Server: rspam08 X-Stat-Signature: 45jkq11dw6h1ccucm5io5b3w8sezhtsy X-HE-Tag: 1773873024-123959 X-HE-Meta: U2FsdGVkX19Hp1yreWDc2MB/dEiWY+mgG0+J5cshHZD+9DI8NAzuEnFeGAiHlnen1RxLaRMQN/caqSTDEl0vmng3kUHlsR3PM6phqmAzp3oAXvqmetY9OQKuKo5TOrDLAUvBfw+QW4cfgqFVNE0K+ddzuzuYo2uiYgzpwQE4po6W8+Z3QlY8BtOTbLu3I177zUGyFNTK2TUNK95VErqDytku7gOKAE/Y/kxbqwRUoFzMPef0jtmQ8k/YQMwYKyOvcNIwLiO7xIvZYe3Kmkv61CXAaYNreT20cR/fr+KPv8MKgM4amv20Gi5sZY+IP1qxWXTV95+VQUrx1krRNtfd0JhmlWP9HncfoEiXr2E93vh+87U2twzIYiAVJNL85icqtm9Abd5Ej1nPcSO6HMh7uJ0RJ8MPgku5Vd6aQiahNfVw4W6iWU3O1F0Lvlr1Q1EcZI3DkQ2coSqZvLCL7yoNO4SpcD41sByvdsgpRb7LBEHh7sE/PghF9JJKh2SVMxWTpvcKT5Pt2sThQPfw6MjQH2kOacJQY91pMzxKoK5kSzJ4dOdD9spQw/L7mEnNXTXPEaNUrVfXt8cReLnaJNxBQt7qg+EoXbn8EbUMin+yWq7UfP27YHg/eKUQ6kybXOHMJq7hlAj8Htlky1+lmL5DoMGiGwFyd/BgkXH2bp7exBnzRvocfw2dETR+Q02/LZp4QlecCIJDTITj3oAs5QVvJZuTYZ0fH0HoudqALi3byBbuML408bNRY45kPGbO8N5PZZgpk+1Ahxa4BW9pn7mwbFufyaTLgiURh8ZOMt3i9C4ScSsXsV94QtnIA1YjHo+CELbr/x09+vzblhVyH/ydnZxlCGCgnw6SILwCH2M2YGSrwb5R04e2IsQgWce/zImXs3SskxRAD45ZC5R8YY0SixcIwDbnVJVJJZPvck3RegLtSDqKpkuzfXhWgs+MOifkByWb5txgyKqqUz3okG6 sMtfC19P 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Zero swap entries are now treated as a separate, decoupled backend in the virtual swap layer. The zeromap bitmap of physical swapfile is no longer used - remove it. This does not have any behavioral change, and save 1 bit per swap page in terms of memory overhead. Signed-off-by: Nhat Pham --- include/linux/swap.h | 1 - mm/swapfile.c | 30 +++++------------------------- 2 files changed, 5 insertions(+), 26 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index fa73696733744..cc1ca4ac2946d 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -260,7 +260,6 @@ struct swap_info_struct { signed char type; /* strange name for an index */ unsigned int max; /* extent of the swap_map */ unsigned char *swap_map; /* vmalloc'ed array of usage counts */ - unsigned long *zeromap; /* kvmalloc'ed bitmap to track zero pages */ struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */ struct list_head free_clusters; /* free clusters list */ struct list_head full_clusters; /* full clusters list */ diff --git a/mm/swapfile.c b/mm/swapfile.c index 32aa080d96a4d..aeb3575df8a0b 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -2320,8 +2320,7 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span) static void setup_swap_info(struct swap_info_struct *si, int prio, unsigned char *swap_map, - struct swap_cluster_info *cluster_info, - unsigned long *zeromap) + struct swap_cluster_info *cluster_info) { si->prio = prio; /* @@ -2332,7 +2331,6 @@ static void setup_swap_info(struct swap_info_struct *si, int prio, si->avail_list.prio = -si->prio; si->swap_map = swap_map; si->cluster_info = cluster_info; - si->zeromap = zeromap; } static void _enable_swap_info(struct swap_info_struct *si) @@ -2350,12 +2348,11 @@ static void _enable_swap_info(struct swap_info_struct *si) static void enable_swap_info(struct swap_info_struct *si, int prio, unsigned char *swap_map, - struct swap_cluster_info *cluster_info, - unsigned long *zeromap) + struct swap_cluster_info *cluster_info) { spin_lock(&swap_lock); spin_lock(&si->lock); - setup_swap_info(si, prio, swap_map, cluster_info, zeromap); + setup_swap_info(si, prio, swap_map, cluster_info); spin_unlock(&si->lock); spin_unlock(&swap_lock); /* @@ -2373,7 +2370,7 @@ static void reinsert_swap_info(struct swap_info_struct *si) { spin_lock(&swap_lock); spin_lock(&si->lock); - setup_swap_info(si, si->prio, si->swap_map, si->cluster_info, si->zeromap); + setup_swap_info(si, si->prio, si->swap_map, si->cluster_info); _enable_swap_info(si); spin_unlock(&si->lock); spin_unlock(&swap_lock); @@ -2444,7 +2441,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) { struct swap_info_struct *p = NULL; unsigned char *swap_map; - unsigned long *zeromap; struct swap_cluster_info *cluster_info; struct file *swap_file, *victim; struct address_space *mapping; @@ -2539,8 +2535,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) p->swap_file = NULL; swap_map = p->swap_map; p->swap_map = NULL; - zeromap = p->zeromap; - p->zeromap = NULL; maxpages = p->max; cluster_info = p->cluster_info; p->max = 0; @@ -2552,7 +2546,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) kfree(p->global_cluster); p->global_cluster = NULL; vfree(swap_map); - kvfree(zeromap); free_cluster_info(cluster_info, maxpages); inode = mapping->host; @@ -3016,7 +3009,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) sector_t span; unsigned long maxpages; unsigned char *swap_map = NULL; - unsigned long *zeromap = NULL; struct swap_cluster_info *cluster_info = NULL; struct folio *folio = NULL; struct inode *inode = NULL; @@ -3122,17 +3114,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) if (error) goto bad_swap_unlock_inode; - /* - * Use kvmalloc_array instead of bitmap_zalloc as the allocation order might - * be above MAX_PAGE_ORDER incase of a large swap file. - */ - zeromap = kvmalloc_array(BITS_TO_LONGS(maxpages), sizeof(long), - GFP_KERNEL | __GFP_ZERO); - if (!zeromap) { - error = -ENOMEM; - goto bad_swap_unlock_inode; - } - if (si->bdev && bdev_stable_writes(si->bdev)) si->flags |= SWP_STABLE_WRITES; @@ -3199,7 +3180,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) prio = DEF_SWAP_PRIO; if (swap_flags & SWAP_FLAG_PREFER) prio = swap_flags & SWAP_FLAG_PRIO_MASK; - enable_swap_info(si, prio, swap_map, cluster_info, zeromap); + enable_swap_info(si, prio, swap_map, cluster_info); pr_info("Adding %uk swap on %s. Priority:%d extents:%d across:%lluk %s%s%s%s\n", K(si->pages), name->name, si->prio, nr_extents, @@ -3227,7 +3208,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) si->flags = 0; spin_unlock(&swap_lock); vfree(swap_map); - kvfree(zeromap); if (cluster_info) free_cluster_info(cluster_info, maxpages); if (inced_nr_rotate_swap) -- 2.52.0