From 5d337b9194b1ce3b6fd5f3cb2799455ed2f9a3d1 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Sat, 3 Sep 2005 15:54:41 -0700 Subject: [PATCH] [PATCH] swap: swap_lock replace list+device The idea of a swap_device_lock per device, and a swap_list_lock over them all, is appealing; but in practice almost every holder of swap_device_lock must already hold swap_list_lock, which defeats the purpose of the split. The only exceptions have been swap_duplicate, valid_swaphandles and an untrodden path in try_to_unuse (plus a few places added in this series). valid_swaphandles doesn't show up high in profiles, but swap_duplicate does demand attention. However, with the hold time in get_swap_pages so much reduced, I've not yet found a load and set of swap device priorities to show even swap_duplicate benefitting from the split. Certainly the split is mere overhead in the common case of a single swap device. So, replace swap_list_lock and swap_device_lock by spinlock_t swap_lock (generally we seem to prefer an _ in the name, and not hide in a macro). If someone can show a regression in swap_duplicate, then probably we should add a hashlock for the swap_map entries alone (shorts being anatomic), so as to help the case of the single swap device too. Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/vm/locking | 15 +++-- include/linux/swap.h | 11 +--- mm/filemap.c | 7 +-- mm/rmap.c | 3 +- mm/swapfile.c | 125 +++++++++++++++++---------------------- 5 files changed, 66 insertions(+), 95 deletions(-) diff --git a/Documentation/vm/locking b/Documentation/vm/locking index c3ef09ae3bb..f366fa95617 100644 --- a/Documentation/vm/locking +++ b/Documentation/vm/locking @@ -83,19 +83,18 @@ single address space optimization, so that the zap_page_range (from vmtruncate) does not lose sending ipi's to cloned threads that might be spawned underneath it and go to user mode to drag in pte's into tlbs. -swap_list_lock/swap_device_lock -------------------------------- +swap_lock +-------------- The swap devices are chained in priority order from the "swap_list" header. The "swap_list" is used for the round-robin swaphandle allocation strategy. The #free swaphandles is maintained in "nr_swap_pages". These two together -are protected by the swap_list_lock. +are protected by the swap_lock. -The swap_device_lock, which is per swap device, protects the reference -counts on the corresponding swaphandles, maintained in the "swap_map" -array, and the "highest_bit" and "lowest_bit" fields. +The swap_lock also protects all the device reference counts on the +corresponding swaphandles, maintained in the "swap_map" array, and the +"highest_bit" and "lowest_bit" fields. -Both of these are spinlocks, and are never acquired from intr level. The -locking hierarchy is swap_list_lock -> swap_device_lock. +The swap_lock is a spinlock, and is never acquired from intr level. To prevent races between swap space deletion or async readahead swapins deciding whether a swap handle is being used, ie worthy of being read in diff --git a/include/linux/swap.h b/include/linux/swap.h index db3b5de7c92..3c9ff004815 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -121,7 +121,7 @@ enum { */ struct swap_info_struct { unsigned int flags; - spinlock_t sdev_lock; + int prio; /* swap priority */ struct file *swap_file; struct block_device *bdev; struct list_head extent_list; @@ -135,7 +135,6 @@ struct swap_info_struct { unsigned int pages; unsigned int max; unsigned int inuse_pages; - int prio; /* swap priority */ int next; /* next entry on swap list */ }; @@ -221,13 +220,7 @@ extern int can_share_swap_page(struct page *); extern int remove_exclusive_swap_page(struct page *); struct backing_dev_info; -extern struct swap_list_t swap_list; -extern spinlock_t swaplock; - -#define swap_list_lock() spin_lock(&swaplock) -#define swap_list_unlock() spin_unlock(&swaplock) -#define swap_device_lock(p) spin_lock(&p->sdev_lock) -#define swap_device_unlock(p) spin_unlock(&p->sdev_lock) +extern spinlock_t swap_lock; /* linux/mm/thrash.c */ extern struct mm_struct * swap_token_mm; diff --git a/mm/filemap.c b/mm/filemap.c index c11418dd94e..edc54436fa9 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -54,9 +54,8 @@ * * ->i_mmap_lock (vmtruncate) * ->private_lock (__free_pte->__set_page_dirty_buffers) - * ->swap_list_lock - * ->swap_device_lock (exclusive_swap_page, others) - * ->mapping->tree_lock + * ->swap_lock (exclusive_swap_page, others) + * ->mapping->tree_lock * * ->i_sem * ->i_mmap_lock (truncate->unmap_mapping_range) @@ -86,7 +85,7 @@ * ->page_table_lock (anon_vma_prepare and various) * * ->page_table_lock - * ->swap_device_lock (try_to_unmap_one) + * ->swap_lock (try_to_unmap_one) * ->private_lock (try_to_unmap_one) * ->tree_lock (try_to_unmap_one) * ->zone.lru_lock (follow_page->mark_page_accessed) diff --git a/mm/rmap.c b/mm/rmap.c index 08ac5c7fa91..facb8cdca66 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -34,9 +34,8 @@ * anon_vma->lock * mm->page_table_lock * zone->lru_lock (in mark_page_accessed) - * swap_list_lock (in swap_free etc's swap_info_get) + * swap_lock (in swap_duplicate, swap_info_get) * mmlist_lock (in mmput, drain_mmlist and others) - * swap_device_lock (in swap_duplicate, swap_info_get) * mapping->private_lock (in __set_page_dirty_buffers) * inode_lock (in set_page_dirty's __mark_inode_dirty) * sb_lock (within inode_lock in fs/fs-writeback.c) diff --git a/mm/swapfile.c b/mm/swapfile.c index e675ae55f87..4b6e8bf986b 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -31,7 +31,7 @@ #include #include -DEFINE_SPINLOCK(swaplock); +DEFINE_SPINLOCK(swap_lock); unsigned int nr_swapfiles; long total_swap_pages; static int swap_overflow; @@ -51,7 +51,7 @@ static DECLARE_MUTEX(swapon_sem); /* * We need this because the bdev->unplug_fn can sleep and we cannot - * hold swap_list_lock while calling the unplug_fn. And swap_list_lock + * hold swap_lock while calling the unplug_fn. And swap_lock * cannot be turned into a semaphore. */ static DECLARE_RWSEM(swap_unplug_sem); @@ -105,7 +105,7 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si) si->cluster_nr = SWAPFILE_CLUSTER - 1; if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) goto lowest; - swap_device_unlock(si); + spin_unlock(&swap_lock); offset = si->lowest_bit; last_in_cluster = offset + SWAPFILE_CLUSTER - 1; @@ -115,7 +115,7 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si) if (si->swap_map[offset]) last_in_cluster = offset + SWAPFILE_CLUSTER; else if (offset == last_in_cluster) { - swap_device_lock(si); + spin_lock(&swap_lock); si->cluster_next = offset-SWAPFILE_CLUSTER-1; goto cluster; } @@ -124,7 +124,7 @@ static inline unsigned long scan_swap_map(struct swap_info_struct *si) latency_ration = LATENCY_LIMIT; } } - swap_device_lock(si); + spin_lock(&swap_lock); goto lowest; } @@ -153,10 +153,10 @@ checks: if (!(si->flags & SWP_WRITEOK)) return offset; } - swap_device_unlock(si); + spin_unlock(&swap_lock); while (++offset <= si->highest_bit) { if (!si->swap_map[offset]) { - swap_device_lock(si); + spin_lock(&swap_lock); goto checks; } if (unlikely(--latency_ration < 0)) { @@ -164,7 +164,7 @@ checks: if (!(si->flags & SWP_WRITEOK)) latency_ration = LATENCY_LIMIT; } } - swap_device_lock(si); + spin_lock(&swap_lock); goto lowest; no_page: @@ -179,7 +179,7 @@ swp_entry_t get_swap_page(void) int type, next; int wrapped = 0; - swap_list_lock(); + spin_lock(&swap_lock); if (nr_swap_pages <= 0) goto noswap; nr_swap_pages--; @@ -199,19 +199,17 @@ swp_entry_t get_swap_page(void) continue; swap_list.next = next; - swap_device_lock(si); - swap_list_unlock(); offset = scan_swap_map(si); - swap_device_unlock(si); - if (offset) + if (offset) { + spin_unlock(&swap_lock); return swp_entry(type, offset); - swap_list_lock(); + } next = swap_list.next; } nr_swap_pages++; noswap: - swap_list_unlock(); + spin_unlock(&swap_lock); return (swp_entry_t) {0}; } @@ -233,8 +231,7 @@ static struct swap_info_struct * swap_info_get(swp_entry_t entry) goto bad_offset; if (!p->swap_map[offset]) goto bad_free; - swap_list_lock(); - swap_device_lock(p); + spin_lock(&swap_lock); return p; bad_free: @@ -252,12 +249,6 @@ out: return NULL; } -static void swap_info_put(struct swap_info_struct * p) -{ - swap_device_unlock(p); - swap_list_unlock(); -} - static int swap_entry_free(struct swap_info_struct *p, unsigned long offset) { int count = p->swap_map[offset]; @@ -290,7 +281,7 @@ void swap_free(swp_entry_t entry) p = swap_info_get(entry); if (p) { swap_entry_free(p, swp_offset(entry)); - swap_info_put(p); + spin_unlock(&swap_lock); } } @@ -308,7 +299,7 @@ static inline int page_swapcount(struct page *page) if (p) { /* Subtract the 1 for the swap cache itself */ count = p->swap_map[swp_offset(entry)] - 1; - swap_info_put(p); + spin_unlock(&swap_lock); } return count; } @@ -365,7 +356,7 @@ int remove_exclusive_swap_page(struct page *page) } write_unlock_irq(&swapper_space.tree_lock); } - swap_info_put(p); + spin_unlock(&swap_lock); if (retval) { swap_free(entry); @@ -388,7 +379,7 @@ void free_swap_and_cache(swp_entry_t entry) if (p) { if (swap_entry_free(p, swp_offset(entry)) == 1) page = find_trylock_page(&swapper_space, entry.val); - swap_info_put(p); + spin_unlock(&swap_lock); } if (page) { int one_user; @@ -558,10 +549,10 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si, int count; /* - * No need for swap_device_lock(si) here: we're just looking + * No need for swap_lock here: we're just looking * for whether an entry is in use, not modifying it; false * hits are okay, and sys_swapoff() has already prevented new - * allocations from this area (while holding swap_list_lock()). + * allocations from this area (while holding swap_lock). */ for (;;) { if (++i >= max) { @@ -751,9 +742,9 @@ static int try_to_unuse(unsigned int type) * report them; but do report if we reset SWAP_MAP_MAX. */ if (*swap_map == SWAP_MAP_MAX) { - swap_device_lock(si); + spin_lock(&swap_lock); *swap_map = 1; - swap_device_unlock(si); + spin_unlock(&swap_lock); reset_overflow = 1; } @@ -817,9 +808,9 @@ static int try_to_unuse(unsigned int type) } /* - * After a successful try_to_unuse, if no swap is now in use, we know we - * can empty the mmlist. swap_list_lock must be held on entry and exit. - * Note that mmlist_lock nests inside swap_list_lock, and an mm must be + * After a successful try_to_unuse, if no swap is now in use, we know + * we can empty the mmlist. swap_lock must be held on entry and exit. + * Note that mmlist_lock nests inside swap_lock, and an mm must be * added to the mmlist just after page_duplicate - before would be racy. */ static void drain_mmlist(void) @@ -1092,7 +1083,7 @@ asmlinkage long sys_swapoff(const char __user * specialfile) mapping = victim->f_mapping; prev = -1; - swap_list_lock(); + spin_lock(&swap_lock); for (type = swap_list.head; type >= 0; type = swap_info[type].next) { p = swap_info + type; if ((p->flags & SWP_ACTIVE) == SWP_ACTIVE) { @@ -1103,14 +1094,14 @@ asmlinkage long sys_swapoff(const char __user * specialfile) } if (type < 0) { err = -EINVAL; - swap_list_unlock(); + spin_unlock(&swap_lock); goto out_dput; } if (!security_vm_enough_memory(p->pages)) vm_unacct_memory(p->pages); else { err = -ENOMEM; - swap_list_unlock(); + spin_unlock(&swap_lock); goto out_dput; } if (prev < 0) { @@ -1124,10 +1115,8 @@ asmlinkage long sys_swapoff(const char __user * specialfile) } nr_swap_pages -= p->pages; total_swap_pages -= p->pages; - swap_device_lock(p); p->flags &= ~SWP_WRITEOK; - swap_device_unlock(p); - swap_list_unlock(); + spin_unlock(&swap_lock); current->flags |= PF_SWAPOFF; err = try_to_unuse(type); @@ -1135,7 +1124,7 @@ asmlinkage long sys_swapoff(const char __user * specialfile) if (err) { /* re-insert swap space back into swap_list */ - swap_list_lock(); + spin_lock(&swap_lock); for (prev = -1, i = swap_list.head; i >= 0; prev = i, i = swap_info[i].next) if (p->prio >= swap_info[i].prio) break; @@ -1146,10 +1135,8 @@ asmlinkage long sys_swapoff(const char __user * specialfile) swap_info[prev].next = p - swap_info; nr_swap_pages += p->pages; total_swap_pages += p->pages; - swap_device_lock(p); p->flags |= SWP_WRITEOK; - swap_device_unlock(p); - swap_list_unlock(); + spin_unlock(&swap_lock); goto out_dput; } @@ -1157,30 +1144,27 @@ asmlinkage long sys_swapoff(const char __user * specialfile) down_write(&swap_unplug_sem); up_write(&swap_unplug_sem); + destroy_swap_extents(p); + down(&swapon_sem); + spin_lock(&swap_lock); + drain_mmlist(); + /* wait for anyone still in scan_swap_map */ - swap_device_lock(p); p->highest_bit = 0; /* cuts scans short */ while (p->flags >= SWP_SCANNING) { - swap_device_unlock(p); + spin_unlock(&swap_lock); set_current_state(TASK_UNINTERRUPTIBLE); schedule_timeout(1); - swap_device_lock(p); + spin_lock(&swap_lock); } - swap_device_unlock(p); - destroy_swap_extents(p); - down(&swapon_sem); - swap_list_lock(); - drain_mmlist(); - swap_device_lock(p); swap_file = p->swap_file; p->swap_file = NULL; p->max = 0; swap_map = p->swap_map; p->swap_map = NULL; p->flags = 0; - swap_device_unlock(p); - swap_list_unlock(); + spin_unlock(&swap_lock); up(&swapon_sem); vfree(swap_map); inode = mapping->host; @@ -1324,7 +1308,7 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags) if (!capable(CAP_SYS_ADMIN)) return -EPERM; - swap_list_lock(); + spin_lock(&swap_lock); p = swap_info; for (type = 0 ; type < nr_swapfiles ; type++,p++) if (!(p->flags & SWP_USED)) @@ -1343,7 +1327,7 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags) * swp_entry_t or the architecture definition of a swap pte. */ if (type > swp_type(pte_to_swp_entry(swp_entry_to_pte(swp_entry(~0UL,0))))) { - swap_list_unlock(); + spin_unlock(&swap_lock); goto out; } if (type >= nr_swapfiles) @@ -1357,7 +1341,6 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags) p->highest_bit = 0; p->cluster_nr = 0; p->inuse_pages = 0; - spin_lock_init(&p->sdev_lock); p->next = -1; if (swap_flags & SWAP_FLAG_PREFER) { p->prio = @@ -1365,7 +1348,7 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags) } else { p->prio = --least_priority; } - swap_list_unlock(); + spin_unlock(&swap_lock); name = getname(specialfile); error = PTR_ERR(name); if (IS_ERR(name)) { @@ -1542,8 +1525,7 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags) } down(&swapon_sem); - swap_list_lock(); - swap_device_lock(p); + spin_lock(&swap_lock); p->flags = SWP_ACTIVE; nr_swap_pages += nr_good_pages; total_swap_pages += nr_good_pages; @@ -1567,8 +1549,7 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags) } else { swap_info[prev].next = p - swap_info; } - swap_device_unlock(p); - swap_list_unlock(); + spin_unlock(&swap_lock); up(&swapon_sem); error = 0; goto out; @@ -1579,14 +1560,14 @@ bad_swap: } destroy_swap_extents(p); bad_swap_2: - swap_list_lock(); + spin_lock(&swap_lock); swap_map = p->swap_map; p->swap_file = NULL; p->swap_map = NULL; p->flags = 0; if (!(swap_flags & SWAP_FLAG_PREFER)) ++least_priority; - swap_list_unlock(); + spin_unlock(&swap_lock); vfree(swap_map); if (swap_file) filp_close(swap_file, NULL); @@ -1610,7 +1591,7 @@ void si_swapinfo(struct sysinfo *val) unsigned int i; unsigned long nr_to_be_unused = 0; - swap_list_lock(); + spin_lock(&swap_lock); for (i = 0; i < nr_swapfiles; i++) { if (!(swap_info[i].flags & SWP_USED) || (swap_info[i].flags & SWP_WRITEOK)) @@ -1619,7 +1600,7 @@ void si_swapinfo(struct sysinfo *val) } val->freeswap = nr_swap_pages + nr_to_be_unused; val->totalswap = total_swap_pages + nr_to_be_unused; - swap_list_unlock(); + spin_unlock(&swap_lock); } /* @@ -1640,7 +1621,7 @@ int swap_duplicate(swp_entry_t entry) p = type + swap_info; offset = swp_offset(entry); - swap_device_lock(p); + spin_lock(&swap_lock); if (offset < p->max && p->swap_map[offset]) { if (p->swap_map[offset] < SWAP_MAP_MAX - 1) { p->swap_map[offset]++; @@ -1652,7 +1633,7 @@ int swap_duplicate(swp_entry_t entry) result = 1; } } - swap_device_unlock(p); + spin_unlock(&swap_lock); out: return result; @@ -1668,7 +1649,7 @@ get_swap_info_struct(unsigned type) } /* - * swap_device_lock prevents swap_map being freed. Don't grab an extra + * swap_lock prevents swap_map being freed. Don't grab an extra * reference on the swaphandle, it doesn't matter if it becomes unused. */ int valid_swaphandles(swp_entry_t entry, unsigned long *offset) @@ -1684,7 +1665,7 @@ int valid_swaphandles(swp_entry_t entry, unsigned long *offset) toff++, i--; *offset = toff; - swap_device_lock(swapdev); + spin_lock(&swap_lock); do { /* Don't read-ahead past the end of the swap area */ if (toff >= swapdev->max) @@ -1697,6 +1678,6 @@ int valid_swaphandles(swp_entry_t entry, unsigned long *offset) toff++; ret++; } while (--i); - swap_device_unlock(swapdev); + spin_unlock(&swap_lock); return ret; } -- 2.20.1