Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932606AbXA1OLk (ORCPT ); Sun, 28 Jan 2007 09:11:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932613AbXA1OLk (ORCPT ); Sun, 28 Jan 2007 09:11:40 -0500 Received: from amsfep15-int.chello.nl ([62.179.120.10]:58869 "EHLO amsfep15-int.chello.nl" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S932606AbXA1OLj (ORCPT ); Sun, 28 Jan 2007 09:11:39 -0500 Subject: [PATCH] mm: remove global locks from mm/highmem.c From: Peter Zijlstra To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Andrew Morton , Ingo Molnar Content-Type: text/plain Date: Sun, 28 Jan 2007 15:11:34 +0100 Message-Id: <1169993494.10987.23.camel@lappy> Mime-Version: 1.0 X-Mailer: Evolution 2.8.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 16886 Lines: 643 Eradicate global locks. - kmap_lock is removed by extensive use of atomic_t, a new flush scheme and modifying set_page_address to only allow NULL<->virt transitions. A count of 0 is an exclusive state acting as an entry lock. This is done using inc_not_zero and cmpxchg. The restriction on changing the virtual address closes the gap with concurrent additions of the same entry. - pool_lock is removed by using the pkmap index for the page_address_maps. By using the pkmap index for the hash entries it is no longer needed to keep a free list. This patch has been in -rt for a while but should also help regular highmem machines with multiple cores/cpus. Signed-off-by: Peter Zijlstra --- include/linux/mm.h | 32 ++- mm/highmem.c | 433 ++++++++++++++++++++++++++++++----------------------- 2 files changed, 276 insertions(+), 189 deletions(-) Index: linux/include/linux/mm.h =================================================================== --- linux.orig/include/linux/mm.h +++ linux/include/linux/mm.h @@ -543,23 +543,39 @@ static __always_inline void *lowmem_page #endif #if defined(WANT_PAGE_VIRTUAL) -#define page_address(page) ((page)->virtual) -#define set_page_address(page, address) \ - do { \ - (page)->virtual = (address); \ - } while(0) -#define page_address_init() do { } while(0) +/* + * wrap page->virtual so it is safe to set/read locklessly + */ +#define page_address(page) \ + ({ typeof((page)->virtual) v = (page)->virtual; \ + smp_read_barrier_depends(); \ + v; }) + +static inline int set_page_address(struct page *page, void *address) +{ + if (address) + return cmpxchg(&page->virtual, NULL, address) == NULL; + else { + /* + * cmpxchg is a bit abused because it is not guaranteed + * safe wrt direct assignment on all platforms. + */ + void *virt = page->virtual; + return cmpxchg(&page->vitrual, virt, NULL) == virt; + } +} +void page_address_init(void); #endif #if defined(HASHED_PAGE_VIRTUAL) void *page_address(struct page *page); -void set_page_address(struct page *page, void *virtual); +int set_page_address(struct page *page, void *virtual); void page_address_init(void); #endif #if !defined(HASHED_PAGE_VIRTUAL) && !defined(WANT_PAGE_VIRTUAL) #define page_address(page) lowmem_page_address(page) -#define set_page_address(page, address) do { } while(0) +#define set_page_address(page, address) (0) #define page_address_init() do { } while(0) #endif Index: linux/mm/highmem.c =================================================================== --- linux.orig/mm/highmem.c +++ linux/mm/highmem.c @@ -14,6 +14,11 @@ * based on Linus' idea. * * Copyright (C) 1999 Ingo Molnar + * + * Largely rewritten to get rid of all global locks + * + * Copyright (C) 2006 Red Hat, Inc., Peter Zijlstra + * */ #include @@ -27,18 +32,14 @@ #include #include #include + #include +#include -/* - * Virtual_count is not a pure "count". - * 0 means that it is not mapped, and has not been mapped - * since a TLB flush - it is usable. - * 1 means that there are no users, but it has been mapped - * since the last TLB flush - so we can't use it. - * n means that there are (n-1) current users of it. - */ #ifdef CONFIG_HIGHMEM +static int __set_page_address(struct page *page, void *virtual, int pos); + unsigned long totalhigh_pages __read_mostly; unsigned int nr_free_highpages (void) @@ -52,164 +53,208 @@ unsigned int nr_free_highpages (void) return pages; } -static int pkmap_count[LAST_PKMAP]; -static unsigned int last_pkmap_nr; -static __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock); +/* + * count is not a pure "count". + * 0 means its owned exclusively by someone + * 1 means its free for use - either mapped or not. + * n means that there are (n-1) current users of it. + */ +static atomic_t pkmap_count[LAST_PKMAP]; +static atomic_t pkmap_hand; pte_t * pkmap_page_table; static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait); -static void flush_all_zero_pkmaps(void) +/* + * Try to free a given kmap slot. + * + * Returns: + * -1 - in use + * 0 - free, no TLB flush needed + * 1 - free, needs TLB flush + */ +static int pkmap_try_free(int pos) { - int i; - - flush_cache_kmaps(); + if (atomic_cmpxchg(&pkmap_count[pos], 1, 0) != 1) + return -1; - for (i = 0; i < LAST_PKMAP; i++) { - struct page *page; + /* + * TODO: add a young bit to make it CLOCK + */ + if (!pte_none(pkmap_page_table[pos])) { + struct page *page = pte_page(pkmap_page_table[pos]); + unsigned long addr = PKMAP_ADDR(pos); + pte_t *ptep = &pkmap_page_table[pos]; + + VM_BUG_ON(addr != (unsigned long)page_address(page)); + + if (!__set_page_address(page, NULL, pos)) + BUG(); + flush_kernel_dcache_page(page); + pte_clear(&init_mm, addr, ptep); - /* - * zero means we don't have anything to do, - * >1 means that it is still in use. Only - * a count of 1 means that it is free but - * needs to be unmapped - */ - if (pkmap_count[i] != 1) - continue; - pkmap_count[i] = 0; + return 1; + } - /* sanity check */ - BUG_ON(pte_none(pkmap_page_table[i])); + return 0; +} - /* - * Don't need an atomic fetch-and-clear op here; - * no-one has the page mapped, and cannot get at - * its virtual address (and hence PTE) without first - * getting the kmap_lock (which is held here). - * So no dangers, even with speculative execution. - */ - page = pte_page(pkmap_page_table[i]); - pte_clear(&init_mm, (unsigned long)page_address(page), - &pkmap_page_table[i]); +static inline void pkmap_put(atomic_t *counter) +{ + switch (atomic_dec_return(counter)) { + case 0: + BUG(); - set_page_address(page, NULL); + case 1: + wake_up(&pkmap_map_wait); } - flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP)); } -static inline unsigned long map_new_virtual(struct page *page) +#define TLB_BATCH 32 + +static int pkmap_get_free(void) { - unsigned long vaddr; - int count; + int i, pos, flush; + DECLARE_WAITQUEUE(wait, current); -start: - count = LAST_PKMAP; - /* Find an empty entry */ - for (;;) { - last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK; - if (!last_pkmap_nr) { - flush_all_zero_pkmaps(); - count = LAST_PKMAP; - } - if (!pkmap_count[last_pkmap_nr]) - break; /* Found a usable entry */ - if (--count) - continue; +restart: + for (i = 0; i < LAST_PKMAP; i++) { + pos = atomic_inc_return(&pkmap_hand) % LAST_PKMAP; + flush = pkmap_try_free(pos); + if (flush >= 0) + goto got_one; + } + + /* + * wait for somebody else to unmap their entries + */ + __set_current_state(TASK_UNINTERRUPTIBLE); + add_wait_queue(&pkmap_map_wait, &wait); + schedule(); + remove_wait_queue(&pkmap_map_wait, &wait); + + goto restart; + +got_one: + if (flush) { +#if 0 + flush_tlb_kernel_range(PKMAP_ADDR(pos), PKMAP_ADDR(pos+1)); +#else + int pos2 = (pos + 1) % LAST_PKMAP; + int nr; + int entries[TLB_BATCH]; /* - * Sleep for somebody else to unmap their entries + * For those architectures that cannot help but flush the + * whole TLB, flush some more entries to make it worthwhile. + * Scan ahead of the hand to minimise search distances. */ - { - DECLARE_WAITQUEUE(wait, current); + for (i = 0, nr = 0; i < LAST_PKMAP && nr < TLB_BATCH; + i++, pos2 = (pos2 + 1) % LAST_PKMAP) { - __set_current_state(TASK_UNINTERRUPTIBLE); - add_wait_queue(&pkmap_map_wait, &wait); - spin_unlock(&kmap_lock); - schedule(); - remove_wait_queue(&pkmap_map_wait, &wait); - spin_lock(&kmap_lock); - - /* Somebody else might have mapped it while we slept */ - if (page_address(page)) - return (unsigned long)page_address(page); + flush = pkmap_try_free(pos2); + if (flush < 0) + continue; + + if (!flush) { + atomic_t *counter = &pkmap_count[pos2]; + VM_BUG_ON(atomic_read(counter) != 0); + atomic_set(counter, 2); + pkmap_put(counter); + } else + entries[nr++] = pos2; + } + flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP)); - /* Re-start */ - goto start; + for (i = 0; i < nr; i++) { + atomic_t *counter = &pkmap_count[entries[i]]; + VM_BUG_ON(atomic_read(counter) != 0); + atomic_set(counter, 2); + pkmap_put(counter); } +#endif } - vaddr = PKMAP_ADDR(last_pkmap_nr); - set_pte_at(&init_mm, vaddr, - &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot)); + return pos; +} + +static unsigned long pkmap_insert(struct page *page) +{ + int pos = pkmap_get_free(); + unsigned long vaddr = PKMAP_ADDR(pos); + pte_t *ptep = &pkmap_page_table[pos]; + pte_t entry = mk_pte(page, kmap_prot); + atomic_t *counter = &pkmap_count[pos]; + + VM_BUG_ON(atomic_read(counter) != 0); - pkmap_count[last_pkmap_nr] = 1; - set_page_address(page, (void *)vaddr); + set_pte_at(&init_mm, vaddr, ptep, entry); + if (unlikely(!__set_page_address(page, (void *)vaddr, pos))) { + /* + * concurrent pkmap_inserts for this page - + * the other won the race, release this entry. + * + * we can still clear the pte without a tlb flush since + * it couldn't have been used yet. + */ + pte_clear(&init_mm, vaddr, ptep); + VM_BUG_ON(atomic_read(counter) != 0); + atomic_set(counter, 2); + pkmap_put(counter); + vaddr = 0; + } else + atomic_set(counter, 2); return vaddr; } -void fastcall *kmap_high(struct page *page) +fastcall void *kmap_high(struct page *page) { unsigned long vaddr; - - /* - * For highmem pages, we can't trust "virtual" until - * after we have the lock. - * - * We cannot call this from interrupts, as it may block - */ - spin_lock(&kmap_lock); +again: vaddr = (unsigned long)page_address(page); + if (vaddr) { + atomic_t *counter = &pkmap_count[PKMAP_NR(vaddr)]; + if (atomic_inc_not_zero(counter)) { + /* + * atomic_inc_not_zero implies a (memory) barrier on success + * so page address will be reloaded. + */ + unsigned long vaddr2 = (unsigned long)page_address(page); + if (likely(vaddr == vaddr2)) + return (void *)vaddr; + + /* + * Oops, we got someone else. + * + * This can happen if we get preempted after + * page_address() and before atomic_inc_not_zero() + * and during that preemption this slot is freed and + * reused. + */ + pkmap_put(counter); + goto again; + } + } + + vaddr = pkmap_insert(page); if (!vaddr) - vaddr = map_new_virtual(page); - pkmap_count[PKMAP_NR(vaddr)]++; - BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2); - spin_unlock(&kmap_lock); - return (void*) vaddr; + goto again; + + return (void *)vaddr; } EXPORT_SYMBOL(kmap_high); -void fastcall kunmap_high(struct page *page) +fastcall void kunmap_high(struct page *page) { - unsigned long vaddr; - unsigned long nr; - int need_wakeup; - - spin_lock(&kmap_lock); - vaddr = (unsigned long)page_address(page); + unsigned long vaddr = (unsigned long)page_address(page); BUG_ON(!vaddr); - nr = PKMAP_NR(vaddr); - - /* - * A count must never go down to zero - * without a TLB flush! - */ - need_wakeup = 0; - switch (--pkmap_count[nr]) { - case 0: - BUG(); - case 1: - /* - * Avoid an unnecessary wake_up() function call. - * The common case is pkmap_count[] == 1, but - * no waiters. - * The tasks queued in the wait-queue are guarded - * by both the lock in the wait-queue-head and by - * the kmap_lock. As the kmap_lock is held here, - * no need for the wait-queue-head's lock. Simply - * test if the queue is empty. - */ - need_wakeup = waitqueue_active(&pkmap_map_wait); - } - spin_unlock(&kmap_lock); - - /* do wake-up, if needed, race-free outside of the spin lock */ - if (need_wakeup) - wake_up(&pkmap_map_wait); + pkmap_put(&pkmap_count[PKMAP_NR(vaddr)]); } EXPORT_SYMBOL(kunmap_high); + #endif #if defined(HASHED_PAGE_VIRTUAL) @@ -217,19 +262,13 @@ EXPORT_SYMBOL(kunmap_high); #define PA_HASH_ORDER 7 /* - * Describes one page->virtual association + * Describes one page->virtual address association. */ -struct page_address_map { +static struct page_address_map { struct page *page; void *virtual; struct list_head list; -}; - -/* - * page_address_map freelist, allocated from page_address_maps. - */ -static struct list_head page_address_pool; /* freelist */ -static spinlock_t pool_lock; /* protects page_address_pool */ +} page_address_maps[LAST_PKMAP]; /* * Hash table bucket @@ -244,91 +283,123 @@ static struct page_address_slot *page_sl return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)]; } -void *page_address(struct page *page) +static void *__page_address(struct page_address_slot *pas, struct page *page) { - unsigned long flags; - void *ret; - struct page_address_slot *pas; - - if (!PageHighMem(page)) - return lowmem_page_address(page); + void *ret = NULL; - pas = page_slot(page); - ret = NULL; - spin_lock_irqsave(&pas->lock, flags); if (!list_empty(&pas->lh)) { struct page_address_map *pam; list_for_each_entry(pam, &pas->lh, list) { if (pam->page == page) { ret = pam->virtual; - goto done; + break; } } } -done: + + return ret; +} + +void *page_address(struct page *page) +{ + unsigned long flags; + void *ret; + struct page_address_slot *pas; + + if (!PageHighMem(page)) + return lowmem_page_address(page); + + pas = page_slot(page); + spin_lock_irqsave(&pas->lock, flags); + ret = __page_address(pas, page); spin_unlock_irqrestore(&pas->lock, flags); return ret; } EXPORT_SYMBOL(page_address); -void set_page_address(struct page *page, void *virtual) +static int __set_page_address(struct page *page, void *virtual, int pos) { + int ret = 0; unsigned long flags; struct page_address_slot *pas; struct page_address_map *pam; - BUG_ON(!PageHighMem(page)); + VM_BUG_ON(!PageHighMem(page)); + VM_BUG_ON(atomic_read(&pkmap_count[pos]) != 0); + VM_BUG_ON(pos < 0 || pos >= LAST_PKMAP); pas = page_slot(page); - if (virtual) { /* Add */ - BUG_ON(list_empty(&page_address_pool)); + pam = &page_address_maps[pos]; - spin_lock_irqsave(&pool_lock, flags); - pam = list_entry(page_address_pool.next, - struct page_address_map, list); - list_del(&pam->list); - spin_unlock_irqrestore(&pool_lock, flags); - - pam->page = page; - pam->virtual = virtual; - - spin_lock_irqsave(&pas->lock, flags); - list_add_tail(&pam->list, &pas->lh); - spin_unlock_irqrestore(&pas->lock, flags); - } else { /* Remove */ - spin_lock_irqsave(&pas->lock, flags); - list_for_each_entry(pam, &pas->lh, list) { - if (pam->page == page) { - list_del(&pam->list); - spin_unlock_irqrestore(&pas->lock, flags); - spin_lock_irqsave(&pool_lock, flags); - list_add_tail(&pam->list, &page_address_pool); - spin_unlock_irqrestore(&pool_lock, flags); - goto done; - } + spin_lock_irqsave(&pas->lock, flags); + if (virtual) { /* add */ + VM_BUG_ON(!list_empty(&pam->list)); + + if (!__page_address(pas, page)) { + pam->page = page; + pam->virtual = virtual; + list_add_tail(&pam->list, &pas->lh); + ret = 1; + } + } else { /* remove */ + if (!list_empty(&pam->list)) { + list_del_init(&pam->list); + ret = 1; } - spin_unlock_irqrestore(&pas->lock, flags); } -done: - return; + spin_unlock_irqrestore(&pas->lock, flags); + + return ret; } -static struct page_address_map page_address_maps[LAST_PKMAP]; +int set_page_address(struct page *page, void *virtual) +{ + /* + * set_page_address is not supposed to be called when using + * hashed virtual addresses. + */ + BUG(); + return 0; +} -void __init page_address_init(void) +void __init __page_address_init(void) { int i; - INIT_LIST_HEAD(&page_address_pool); for (i = 0; i < ARRAY_SIZE(page_address_maps); i++) - list_add(&page_address_maps[i].list, &page_address_pool); + INIT_LIST_HEAD(&page_address_maps[i].list); + for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) { INIT_LIST_HEAD(&page_address_htable[i].lh); spin_lock_init(&page_address_htable[i].lock); } - spin_lock_init(&pool_lock); +} + +#elif defined (CONFIG_HIGHMEM) /* HASHED_PAGE_VIRTUAL */ + +static int __set_page_address(struct page *page, void *virtual, int pos) +{ + return set_page_address(page, virtual); } #endif /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */ + +#if defined(CONFIG_HIGHMEM) || defined(HASHED_PAGE_VIRTUAL) + +void __init page_address_init(void) +{ +#ifdef CONFIG_HIGHMEM + int i; + + for (i = 0; i < ARRAY_SIZE(pkmap_count); i++) + atomic_set(&pkmap_count[i], 1); +#endif + +#ifdef HASHED_PAGE_VIRTUAL + __page_address_init(); +#endif +} + +#endif - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/