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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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) =20 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 =3D prio; /* @@ -2332,7 +2331,6 @@ static void setup_swap_info(struct swap_info_struct *= si, int prio, si->avail_list.prio =3D -si->prio; si->swap_map =3D swap_map; si->cluster_info =3D cluster_info; - si->zeromap =3D zeromap; } =20 static void _enable_swap_info(struct swap_info_struct *si) @@ -2350,12 +2348,11 @@ static void _enable_swap_info(struct swap_info_stru= ct *si) =20 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_struc= t *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 *, special= file) { struct swap_info_struct *p =3D 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 *, special= file) p->swap_file =3D NULL; swap_map =3D p->swap_map; p->swap_map =3D NULL; - zeromap =3D p->zeromap; - p->zeromap =3D NULL; maxpages =3D p->max; cluster_info =3D p->cluster_info; p->max =3D 0; @@ -2552,7 +2546,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, special= file) kfree(p->global_cluster); p->global_cluster =3D NULL; vfree(swap_map); - kvfree(zeromap); free_cluster_info(cluster_info, maxpages); =20 inode =3D mapping->host; @@ -3016,7 +3009,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialf= ile, int, swap_flags) sector_t span; unsigned long maxpages; unsigned char *swap_map =3D NULL; - unsigned long *zeromap =3D NULL; struct swap_cluster_info *cluster_info =3D NULL; struct folio *folio =3D NULL; struct inode *inode =3D NULL; @@ -3122,17 +3114,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, special= file, int, swap_flags) if (error) goto bad_swap_unlock_inode; =20 - /* - * Use kvmalloc_array instead of bitmap_zalloc as the allocation order mi= ght - * be above MAX_PAGE_ORDER incase of a large swap file. - */ - zeromap =3D kvmalloc_array(BITS_TO_LONGS(maxpages), sizeof(long), - GFP_KERNEL | __GFP_ZERO); - if (!zeromap) { - error =3D -ENOMEM; - goto bad_swap_unlock_inode; - } - if (si->bdev && bdev_stable_writes(si->bdev)) si->flags |=3D SWP_STABLE_WRITES; =20 @@ -3199,7 +3180,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialf= ile, int, swap_flags) prio =3D DEF_SWAP_PRIO; if (swap_flags & SWAP_FLAG_PREFER) prio =3D 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); =20 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 *, specialf= ile, int, swap_flags) si->flags =3D 0; spin_unlock(&swap_lock); vfree(swap_map); - kvfree(zeromap); if (cluster_info) free_cluster_info(cluster_info, maxpages); if (inced_nr_rotate_swap) --=20 2.52.0