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[82.53.214.132]) by smtp.gmail.com with ESMTPSA id t15-20020a1709063e4f00b00965c529f103sm5619618eji.86.2023.06.06.07.56.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Jun 2023 07:56:39 -0700 (PDT) From: Domenico Cerasuolo To: vitaly.wool@konsulko.com, minchan@kernel.org, senozhatsky@chromium.org, yosryahmed@google.com, linux-mm@kvack.org Cc: ddstreet@ieee.org, sjenning@redhat.com, nphamcs@gmail.com, hannes@cmpxchg.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, Domenico Cerasuolo Subject: [RFC PATCH v2 2/7] mm: zswap: remove page reclaim logic from zbud Date: Tue, 6 Jun 2023 16:56:06 +0200 Message-Id: <20230606145611.704392-3-cerasuolodomenico@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230606145611.704392-1-cerasuolodomenico@gmail.com> References: <20230606145611.704392-1-cerasuolodomenico@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" With the recent enhancement to zswap enabling direct page writeback, the need for the shrink code in zbud has become obsolete. As a result, this commit removes the page reclaim logic from zbud entirely. Signed-off-by: Domenico Cerasuolo Acked-by: Johannes Weiner --- mm/zbud.c | 164 +----------------------------------------------------- 1 file changed, 2 insertions(+), 162 deletions(-) diff --git a/mm/zbud.c b/mm/zbud.c index 3acd26193920..19bc662ef5e9 100644 --- a/mm/zbud.c +++ b/mm/zbud.c @@ -83,11 +83,7 @@ struct zbud_pool; * its free region. * @buddied: list tracking the zbud pages that contain two buddies; * these zbud pages are full - * @lru: list tracking the zbud pages in LRU order by most recently - * added buddy. * @pages_nr: number of zbud pages in the pool. - * @zpool: zpool driver - * @zpool_ops: zpool operations structure with an evict callback * * This structure is allocated at pool creation time and maintains metadata * pertaining to a particular zbud pool. @@ -102,26 +98,20 @@ struct zbud_pool { struct list_head buddied; struct list_head unbuddied[NCHUNKS]; }; - struct list_head lru; u64 pages_nr; - struct zpool *zpool; - const struct zpool_ops *zpool_ops; }; =20 /* * struct zbud_header - zbud page metadata occupying the first chunk of ea= ch * zbud page. * @buddy: links the zbud page into the unbuddied/buddied lists in the pool - * @lru: links the zbud page into the lru list in the pool * @first_chunks: the size of the first buddy in chunks, 0 if free * @last_chunks: the size of the last buddy in chunks, 0 if free */ struct zbud_header { struct list_head buddy; - struct list_head lru; unsigned int first_chunks; unsigned int last_chunks; - bool under_reclaim; }; =20 /***************** @@ -149,8 +139,6 @@ static struct zbud_header *init_zbud_page(struct page *= page) zhdr->first_chunks =3D 0; zhdr->last_chunks =3D 0; INIT_LIST_HEAD(&zhdr->buddy); - INIT_LIST_HEAD(&zhdr->lru); - zhdr->under_reclaim =3D false; return zhdr; } =20 @@ -221,7 +209,6 @@ static struct zbud_pool *zbud_create_pool(gfp_t gfp) for_each_unbuddied_list(i, 0) INIT_LIST_HEAD(&pool->unbuddied[i]); INIT_LIST_HEAD(&pool->buddied); - INIT_LIST_HEAD(&pool->lru); pool->pages_nr =3D 0; return pool; } @@ -310,11 +297,6 @@ static int zbud_alloc(struct zbud_pool *pool, size_t s= ize, gfp_t gfp, list_add(&zhdr->buddy, &pool->buddied); } =20 - /* Add/move zbud page to beginning of LRU */ - if (!list_empty(&zhdr->lru)) - list_del(&zhdr->lru); - list_add(&zhdr->lru, &pool->lru); - *handle =3D encode_handle(zhdr, bud); spin_unlock(&pool->lock); =20 @@ -325,11 +307,6 @@ static int zbud_alloc(struct zbud_pool *pool, size_t s= ize, gfp_t gfp, * zbud_free() - frees the allocation associated with the given handle * @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). */ static void zbud_free(struct zbud_pool *pool, unsigned long handle) { @@ -345,18 +322,11 @@ static void zbud_free(struct zbud_pool *pool, unsigne= d long handle) else zhdr->first_chunks =3D 0; =20 - 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); =20 if (zhdr->first_chunks =3D=3D 0 && zhdr->last_chunks =3D=3D 0) { /* zbud page is empty, free */ - list_del(&zhdr->lru); free_zbud_page(zhdr); pool->pages_nr--; } else { @@ -368,110 +338,6 @@ static void zbud_free(struct zbud_pool *pool, unsigne= d long handle) spin_unlock(&pool->lock); } =20 -/** - * zbud_reclaim_page() - evicts allocations from a pool page and frees it - * @pool: pool from which a page will attempt to be evicted - * @retries: number of pages on the LRU list for which eviction will - * be attempted before failing - * - * zbud reclaim is different from normal system reclaim in that the reclai= m is - * done from the bottom, up. This is because only the bottom layer, zbud,= has - * information on how the allocations are organized within each zbud page.= This - * has the potential to create interesting locking situations between zbud= and - * the user, however. - * - * 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. - * - * 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 - * 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 pa= ge. - * - * If all buddies in the zbud page are successfully evicted, then the - * zbud page can be freed. - * - * 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 - * the retry limit was hit. - */ -static int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries) -{ - int i, ret, freechunks; - struct zbud_header *zhdr; - unsigned long first_handle =3D 0, last_handle =3D 0; - - spin_lock(&pool->lock); - if (list_empty(&pool->lru)) { - spin_unlock(&pool->lock); - return -EINVAL; - } - for (i =3D 0; i < retries; i++) { - zhdr =3D list_last_entry(&pool->lru, struct zbud_header, lru); - list_del(&zhdr->lru); - list_del(&zhdr->buddy); - /* Protect zbud page against free */ - zhdr->under_reclaim =3D true; - /* - * We need encode the handles before unlocking, since we can - * race with free that will set (first|last)_chunks to 0 - */ - first_handle =3D 0; - last_handle =3D 0; - if (zhdr->first_chunks) - first_handle =3D encode_handle(zhdr, FIRST); - if (zhdr->last_chunks) - last_handle =3D encode_handle(zhdr, LAST); - spin_unlock(&pool->lock); - - /* Issue the eviction callback(s) */ - if (first_handle) { - ret =3D pool->zpool_ops->evict(pool->zpool, first_handle); - if (ret) - goto next; - } - if (last_handle) { - ret =3D pool->zpool_ops->evict(pool->zpool, last_handle); - if (ret) - goto next; - } -next: - spin_lock(&pool->lock); - zhdr->under_reclaim =3D false; - if (zhdr->first_chunks =3D=3D 0 && zhdr->last_chunks =3D=3D 0) { - /* - * Both buddies are now free, free the zbud page and - * return success. - */ - free_zbud_page(zhdr); - pool->pages_nr--; - spin_unlock(&pool->lock); - return 0; - } else if (zhdr->first_chunks =3D=3D 0 || - zhdr->last_chunks =3D=3D 0) { - /* add to unbuddied list */ - freechunks =3D 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_unlock(&pool->lock); - return -EAGAIN; -} - /** * zbud_map() - maps the allocation associated with the given handle * @pool: pool in which the allocation resides @@ -518,14 +384,7 @@ static void *zbud_zpool_create(const char *name, gfp_t= gfp, const struct zpool_ops *zpool_ops, struct zpool *zpool) { - struct zbud_pool *pool; - - pool =3D zbud_create_pool(gfp); - if (pool) { - pool->zpool =3D zpool; - pool->zpool_ops =3D zpool_ops; - } - return pool; + return zbud_create_pool(gfp); } =20 static void zbud_zpool_destroy(void *pool) @@ -543,25 +402,6 @@ static void zbud_zpool_free(void *pool, unsigned long = handle) zbud_free(pool, handle); } =20 -static int zbud_zpool_shrink(void *pool, unsigned int pages, - unsigned int *reclaimed) -{ - unsigned int total =3D 0; - int ret =3D -EINVAL; - - while (total < pages) { - ret =3D zbud_reclaim_page(pool, 8); - if (ret < 0) - break; - total++; - } - - if (reclaimed) - *reclaimed =3D total; - - return ret; -} - static void *zbud_zpool_map(void *pool, unsigned long handle, enum zpool_mapmode mm) { @@ -585,7 +425,7 @@ static struct zpool_driver zbud_zpool_driver =3D { .destroy =3D zbud_zpool_destroy, .malloc =3D zbud_zpool_malloc, .free =3D zbud_zpool_free, - .shrink =3D zbud_zpool_shrink, + .shrink =3D NULL, .map =3D zbud_zpool_map, .unmap =3D zbud_zpool_unmap, .total_size =3D zbud_zpool_total_size, --=20 2.34.1