Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753431Ab3IKJAX (ORCPT ); Wed, 11 Sep 2013 05:00:23 -0400 Received: from mailout4.w1.samsung.com ([210.118.77.14]:47123 "EHLO mailout4.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752042Ab3IKI7Q (ORCPT ); Wed, 11 Sep 2013 04:59:16 -0400 X-AuditID: cbfec7f5-b7ef66d00000795a-27-523030e23456 From: Krzysztof Kozlowski To: Seth Jennings , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Cc: Bob Liu , Mel Gorman , Bartlomiej Zolnierkiewicz , Marek Szyprowski , Kyungmin Park , Dave Hansen , Minchan Kim , Krzysztof Kozlowski , Tomasz Stanislawski Subject: [PATCH v2 1/5] zbud: use page ref counter for zbud pages Date: Wed, 11 Sep 2013 10:59:00 +0200 Message-id: <1378889944-23192-2-git-send-email-k.kozlowski@samsung.com> X-Mailer: git-send-email 1.7.9.5 In-reply-to: <1378889944-23192-1-git-send-email-k.kozlowski@samsung.com> References: <1378889944-23192-1-git-send-email-k.kozlowski@samsung.com> X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrCLMWRmVeSWpSXmKPExsVy+t/xq7qPDAyCDNreSVnMWb+GzWLjjPWs Fl2nprJYfHr5gNHi9QtDi7NNb9gtLu+aw2Zxb81/Vou1R+6yW0x+94zRYtnX9+wWh/atYreY 1/6S1YHXY/Gel0wem1Z1snls+jSJ3ePEjN8sHg8ObWbx+Pj0FotH35ZVjB6bT1d7fN4kF8AZ xWWTkpqTWZZapG+XwJXxacFj5oLlThUv9kxmbGDcZNLFyMkhIWAised1IwuELSZx4d56ti5G Lg4hgaWMEs2HmpkgnD4miS/XNzKCVLEJGEtsXr6EDcQWEehjlJh02QKkiFngH5NEx/s5YAlh AUeJvstfWbsYOThYBFQlni9LAwnzCrhLrNuwBCwsIaAgMWeSDYjJKeAhcWKaAkiFEFBF569z bBMYeRcwMqxiFE0tTS4oTkrPNdIrTswtLs1L10vOz93ECAnZrzsYlx6zOsQowMGoxMNroKgf JMSaWFZcmXuIUYKDWUmE95WoQZAQb0piZVVqUX58UWlOavEhRiYOTqkGxownGi3rDi4Ru/55 YXThtaUMB0NrKr/sv6Z2uyr57fnWUIcwDzaVlRd/ec/4vvlR9+bkK5n2384d/JoVfX6V/R7/ wDcfLOyDvtkl37Z+O10rwyvOrOSGpPKX5gWqD5V3vJyoNZ8tzthTVISJtVfSOD7wt4JZM09P bvn5X1K/L35K6HlbdKTplxJLcUaioRZzUXEiAKh4CjE3AgAA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8489 Lines: 248 Use page reference counter for zbud pages. The ref counter replaces zbud_header.under_reclaim flag and ensures that zbud page won't be freed when zbud_free() is called during reclaim. It allows implementation of additional reclaim paths. The page count is incremented when: - a handle is created and passed to zswap (in zbud_alloc()), - user-supplied eviction callback is called (in zbud_reclaim_page()). Signed-off-by: Krzysztof Kozlowski Signed-off-by: Tomasz Stanislawski Reviewed-by: Bob Liu --- mm/zbud.c | 117 +++++++++++++++++++++++++++++++++---------------------------- 1 file changed, 64 insertions(+), 53 deletions(-) diff --git a/mm/zbud.c b/mm/zbud.c index ad1e781..3f4be72 100644 --- a/mm/zbud.c +++ b/mm/zbud.c @@ -109,7 +109,6 @@ struct zbud_header { struct list_head lru; unsigned int first_chunks; unsigned int last_chunks; - bool under_reclaim; }; /***************** @@ -138,16 +137,9 @@ static struct zbud_header *init_zbud_page(struct page *page) zhdr->last_chunks = 0; INIT_LIST_HEAD(&zhdr->buddy); INIT_LIST_HEAD(&zhdr->lru); - zhdr->under_reclaim = 0; return zhdr; } -/* Resets the struct page fields and frees the page */ -static void free_zbud_page(struct zbud_header *zhdr) -{ - __free_page(virt_to_page(zhdr)); -} - /* * Encodes the handle of a particular buddy within a zbud page * Pool lock should be held as this function accesses first|last_chunks @@ -188,6 +180,31 @@ static int num_free_chunks(struct zbud_header *zhdr) return NCHUNKS - zhdr->first_chunks - zhdr->last_chunks - 1; } +/* + * Increases ref count for zbud page. + */ +static void get_zbud_page(struct zbud_header *zhdr) +{ + get_page(virt_to_page(zhdr)); +} + +/* + * Decreases ref count for zbud page and frees the page if it reaches 0 + * (no external references, e.g. handles). + * + * Returns 1 if page was freed and 0 otherwise. + */ +static int put_zbud_page(struct zbud_header *zhdr) +{ + struct page *page = virt_to_page(zhdr); + if (put_page_testzero(page)) { + free_hot_cold_page(page, 0); + return 1; + } + return 0; +} + + /***************** * API Functions *****************/ @@ -273,6 +290,7 @@ int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp, bud = FIRST; else bud = LAST; + get_zbud_page(zhdr); goto found; } } @@ -284,6 +302,10 @@ int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp, return -ENOMEM; spin_lock(&pool->lock); pool->pages_nr++; + /* + * We will be using zhdr instead of page, so + * don't increase the page count. + */ zhdr = init_zbud_page(page); bud = FIRST; @@ -318,10 +340,11 @@ found: * @pool: pool in which the allocation resided * @handle: handle associated with the allocation returned by zbud_alloc() * - * In the case that the zbud page in which the allocation resides is under - * reclaim, as indicated by the PG_reclaim flag being set, this function - * only sets the first|last_chunks to 0. The page is actually freed - * once both buddies are evicted (see zbud_reclaim_page() below). + * This function sets first|last_chunks to 0, removes zbud header from + * appropriate lists (LRU, buddied/unbuddied) and puts the reference count + * for it. The page is actually freed once both buddies are evicted + * (zbud_free() called on both handles or page reclaim in zbud_reclaim_page() + * below). */ void zbud_free(struct zbud_pool *pool, unsigned long handle) { @@ -337,19 +360,11 @@ void zbud_free(struct zbud_pool *pool, unsigned long handle) else zhdr->first_chunks = 0; - if (zhdr->under_reclaim) { - /* zbud page is under reclaim, reclaim will free */ - spin_unlock(&pool->lock); - return; - } - /* Remove from existing buddy list */ list_del(&zhdr->buddy); if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) { - /* zbud page is empty, free */ list_del(&zhdr->lru); - free_zbud_page(zhdr); pool->pages_nr--; } else { /* Add to unbuddied list */ @@ -357,6 +372,7 @@ void zbud_free(struct zbud_pool *pool, unsigned long handle) list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); } + put_zbud_page(zhdr); spin_unlock(&pool->lock); } @@ -378,21 +394,23 @@ void zbud_free(struct zbud_pool *pool, unsigned long handle) * To avoid these, this is how zbud_reclaim_page() should be called: * The user detects a page should be reclaimed and calls zbud_reclaim_page(). - * zbud_reclaim_page() will remove a zbud page from the pool LRU list and call - * the user-defined eviction handler with the pool and handle as arguments. + * zbud_reclaim_page() will move zbud page to the beginning of the pool + * LRU list, increase the page reference count and call the user-defined + * eviction handler with the pool and handle as arguments. * * If the handle can not be evicted, the eviction handler should return - * non-zero. zbud_reclaim_page() will add the zbud page back to the - * appropriate list and try the next zbud page on the LRU up to + * non-zero. zbud_reclaim_page() will drop the reference count for page + * obtained earlier and try the next zbud page on the LRU up to * a user defined number of retries. * * If the handle is successfully evicted, the eviction handler should * return 0 _and_ should have called zbud_free() on the handle. zbud_free() - * contains logic to delay freeing the page if the page is under reclaim, - * as indicated by the setting of the PG_reclaim flag on the underlying page. + * will remove the page from appropriate lists (LRU, buddied/unbuddied) and + * drop the reference count associated with given handle. + * Then the zbud_reclaim_page() will drop reference count obtained earlier. * - * If all buddies in the zbud page are successfully evicted, then the - * zbud page can be freed. + * If all buddies in the zbud page are successfully evicted, then dropping + * this last reference count will free the page. * * Returns: 0 if page is successfully freed, otherwise -EINVAL if there are * no pages to evict or an eviction handler is not registered, -EAGAIN if @@ -400,7 +418,7 @@ void zbud_free(struct zbud_pool *pool, unsigned long handle) */ int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries) { - int i, ret, freechunks; + int i, ret; struct zbud_header *zhdr; unsigned long first_handle = 0, last_handle = 0; @@ -411,11 +429,24 @@ int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries) return -EINVAL; } for (i = 0; i < retries; i++) { + if (list_empty(&pool->lru)) { + /* + * LRU was emptied during evict calls in previous + * iteration but put_zbud_page() returned 0 meaning + * that someone still holds the page. This may + * happen when some other mm mechanism increased + * the page count. + * In such case we succedded with reclaim. + */ + spin_unlock(&pool->lock); + return 0; + } zhdr = list_tail_entry(&pool->lru, struct zbud_header, lru); + /* Move this last element to beginning of LRU */ list_del(&zhdr->lru); - list_del(&zhdr->buddy); + list_add(&zhdr->lru, &pool->lru); /* Protect zbud page against free */ - zhdr->under_reclaim = true; + get_zbud_page(zhdr); /* * We need encode the handles before unlocking, since we can * race with free that will set (first|last)_chunks to 0 @@ -440,29 +471,9 @@ int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries) goto next; } next: - spin_lock(&pool->lock); - zhdr->under_reclaim = false; - if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) { - /* - * Both buddies are now free, free the zbud page and - * return success. - */ - free_zbud_page(zhdr); - pool->pages_nr--; - spin_unlock(&pool->lock); + if (put_zbud_page(zhdr)) return 0; - } else if (zhdr->first_chunks == 0 || - zhdr->last_chunks == 0) { - /* add to unbuddied list */ - freechunks = num_free_chunks(zhdr); - list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); - } else { - /* add to buddied list */ - list_add(&zhdr->buddy, &pool->buddied); - } - - /* add to beginning of LRU */ - list_add(&zhdr->lru, &pool->lru); + spin_lock(&pool->lock); } spin_unlock(&pool->lock); return -EAGAIN; -- 1.7.9.5 -- 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/