zswap_store() will store large folios by compressing them page by page. This patch provides a sequential implementation of storing a large folio in zswap_store() by iterating through each page in the folio to compress and store it in the zswap zpool. Towards this goal, zswap_compress() is modified to take a page instead of a folio as input. Each page's swap offset is stored as a separate zswap entry. We check the cgroup zswap limit and the zpool utilization against the zswap max/accept_threshold limits once, at the beginning of zswap_store. We also obtain a percpu_ref_tryget() reference to the current zswap_pool at the start of zswap_store to prevent it from being deleted while the folio is being stored. If these one-time checks pass, we compress the sub-pages of the folio, while maintaining a running count of compressed bytes for all the folio's sub-pages. If all pages are successfully compressed and stored, we do the cgroup zswap charging with the total compressed bytes, and batch update the zswap_stored_pages atomic/zswpout event stats with folio_nr_pages() once, before returning from zswap_store. The patch adds a new zswap_pool_get() function that is called in the sub-page level "zswap_store_page()" function. If an error is encountered during the store of any page in the folio, all pages in that folio currently stored in zswap will be invalidated. Thus, a folio is either entirely stored in zswap, or entirely not stored in zswap. This patch forms the basis for building compress batching of pages in a large folio in zswap_store by compressing up to say, 8 pages of the folio in parallel in hardware using the Intel In-Memory Analytics Accelerator (Intel IAA). This change reuses and adapts the functionality in Ryan Roberts' RFC patch [1]: "[RFC,v1] mm: zswap: Store large folios without splitting" [1] https://lore.kernel.org/linux-mm/20231019110543.3284654-1-ryan.roberts@xxxxxxx/T/#u Also, addressed some of the RFC comments from the discussion in [1]. Co-developed-by: Ryan Roberts Signed-off-by: Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx> --- mm/zswap.c | 227 ++++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 165 insertions(+), 62 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index 43e4e216db41..b8395ddf7b7c 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -411,6 +411,16 @@ static int __must_check zswap_pool_tryget(struct zswap_pool *pool) return percpu_ref_tryget(&pool->ref); } +/* + * Note: zswap_pool_get() should only be called after zswap_pool_tryget() + * returns success. zswap_pool_tryget() returns success only if the "pool" is + * non-NULL and the "&pool->ref" is non-0. + */ +static void zswap_pool_get(struct zswap_pool *pool) +{ + percpu_ref_get(&pool->ref); +} + static void zswap_pool_put(struct zswap_pool *pool) { percpu_ref_put(&pool->ref); @@ -1402,38 +1412,35 @@ static void shrink_worker(struct work_struct *w) /********************************* * main API **********************************/ -bool zswap_store(struct folio *folio) + +/* + * Stores the page at specified "index" in a folio. + * + * @folio: The folio to store in zswap. + * @index: Index into the page in the folio that this function will store. + * @objcg: The folio's objcg. + * @pool: The zswap_pool to store the compressed data for the page. + * The caller should have obtained a reference to a valid + * zswap_pool by calling zswap_pool_tryget(), to pass as this + * argument. + * @compressed_bytes: The compressed entry->length value is added + * to this, so that the caller can get the total + * compressed lengths of all sub-pages in a folio. + */ +static bool zswap_store_page(struct folio *folio, long index, + struct obj_cgroup *objcg, + struct zswap_pool *pool, + size_t *compressed_bytes) { + struct page *page = folio_page(folio, index); swp_entry_t swp = folio->swap; - pgoff_t offset = swp_offset(swp); struct xarray *tree = swap_zswap_tree(swp); + pgoff_t offset = swp_offset(swp) + index; struct zswap_entry *entry, *old; - struct obj_cgroup *objcg = NULL; - struct mem_cgroup *memcg = NULL; - - VM_WARN_ON_ONCE(!folio_test_locked(folio)); - VM_WARN_ON_ONCE(!folio_test_swapcache(folio)); + int type = swp_type(swp); - /* Large folios aren't supported */ - if (folio_test_large(folio)) - return false; - - if (!zswap_enabled) - goto check_old; - - /* Check cgroup limits */ - objcg = get_obj_cgroup_from_folio(folio); - if (objcg && !obj_cgroup_may_zswap(objcg)) { - memcg = get_mem_cgroup_from_objcg(objcg); - if (shrink_memcg(memcg)) { - mem_cgroup_put(memcg); - goto reject; - } - mem_cgroup_put(memcg); - } - - if (zswap_check_limits()) - goto reject; + if (objcg) + obj_cgroup_get(objcg); /* allocate entry */ entry = zswap_entry_cache_alloc(GFP_KERNEL, folio_nid(folio)); @@ -1442,24 +1449,21 @@ bool zswap_store(struct folio *folio) goto reject; } - /* if entry is successfully added, it keeps the reference */ - entry->pool = zswap_pool_current_get(); - if (!entry->pool) - goto freepage; + /* + * We get here only after the call to zswap_pool_tryget() in the + * caller, zswap_store(), has returned success. Hence it is safe + * to call zswap_pool_get(). + * + * if entry is successfully added, it keeps the reference + */ + zswap_pool_get(pool); - if (objcg) { - memcg = get_mem_cgroup_from_objcg(objcg); - if (memcg_list_lru_alloc(memcg, &zswap_list_lru, GFP_KERNEL)) { - mem_cgroup_put(memcg); - goto put_pool; - } - mem_cgroup_put(memcg); - } + entry->pool = pool; - if (!zswap_compress(&folio->page, entry)) + if (!zswap_compress(page, entry)) goto put_pool; - entry->swpentry = swp; + entry->swpentry = swp_entry(type, offset); entry->objcg = objcg; entry->referenced = true; @@ -1480,11 +1484,6 @@ bool zswap_store(struct folio *folio) if (old) zswap_entry_free(old); - if (objcg) { - obj_cgroup_charge_zswap(objcg, entry->length); - count_objcg_event(objcg, ZSWPOUT); - } - /* * We finish initializing the entry while it's already in xarray. * This is safe because: @@ -1496,36 +1495,140 @@ bool zswap_store(struct folio *folio) * an incoherent entry. */ if (entry->length) { + *compressed_bytes += entry->length; INIT_LIST_HEAD(&entry->lru); zswap_lru_add(&zswap_list_lru, entry); } - /* update stats */ - atomic_long_inc(&zswap_stored_pages); - count_vm_event(ZSWPOUT); - return true; store_failed: zpool_free(entry->pool->zpool, entry->handle); put_pool: - zswap_pool_put(entry->pool); -freepage: + zswap_pool_put(pool); zswap_entry_cache_free(entry); reject: obj_cgroup_put(objcg); - if (zswap_pool_reached_full) - queue_work(shrink_wq, &zswap_shrink_work); -check_old: + return false; +} + +bool zswap_store(struct folio *folio) +{ + long nr_pages = folio_nr_pages(folio); + swp_entry_t swp = folio->swap; + struct xarray *tree = swap_zswap_tree(swp); + pgoff_t offset = swp_offset(swp); + struct obj_cgroup *objcg = NULL; + struct mem_cgroup *memcg = NULL; + struct zswap_pool *pool; + size_t compressed_bytes = 0; + bool ret = false; + long index; + + VM_WARN_ON_ONCE(!folio_test_locked(folio)); + VM_WARN_ON_ONCE(!folio_test_swapcache(folio)); + + if (!zswap_enabled) + goto reject; + /* - * If the zswap store fails or zswap is disabled, we must invalidate the - * possibly stale entry which was previously stored at this offset. - * Otherwise, writeback could overwrite the new data in the swapfile. + * Check cgroup zswap limits: + * + * The cgroup zswap limit check is done once at the beginning of + * zswap_store(). The cgroup charging is done once, at the end + * of a successful folio store. What this means is, if the cgroup + * was within the zswap_max limit at the beginning of a large folio + * store, it could go over the limit by at most (HPAGE_PMD_NR - 1) + * pages. */ - entry = xa_erase(tree, offset); - if (entry) - zswap_entry_free(entry); - return false; + objcg = get_obj_cgroup_from_folio(folio); + if (objcg && !obj_cgroup_may_zswap(objcg)) { + memcg = get_mem_cgroup_from_objcg(objcg); + if (shrink_memcg(memcg)) { + mem_cgroup_put(memcg); + goto put_objcg; + } + mem_cgroup_put(memcg); + } + + /* + * Check zpool utilization against zswap limits: + * + * The zswap zpool utilization is also checked against the limits + * just once, at the start of zswap_store(). If the check passes, + * any breaches of the limits set by zswap_max_pages() or + * zswap_accept_thr_pages() that may happen while storing this + * folio, will only be detected during the next call to + * zswap_store() by any process. + */ + if (zswap_check_limits()) + goto put_objcg; + + pool = zswap_pool_current_get(); + if (!pool) + goto put_objcg; + + if (objcg) { + memcg = get_mem_cgroup_from_objcg(objcg); + if (memcg_list_lru_alloc(memcg, &zswap_list_lru, GFP_KERNEL)) { + mem_cgroup_put(memcg); + goto put_pool; + } + mem_cgroup_put(memcg); + } + + /* + * Store each page of the folio as a separate entry. If we fail to + * store a page, unwind by deleting all the pages for this folio + * currently in zswap. + */ + for (index = 0; index < nr_pages; ++index) { + if (!zswap_store_page(folio, index, objcg, pool, &compressed_bytes)) + goto put_pool; + } + + /* + * All pages in the folio have been successfully stored. + * Batch update the cgroup zswap charging, zswap_stored_page atomic, + * and ZSWPOUT event stats. + */ + if (objcg) { + obj_cgroup_charge_zswap(objcg, compressed_bytes); + count_objcg_events(objcg, ZSWPOUT, nr_pages); + } + + /* update stats */ + atomic_long_add(nr_pages, &zswap_stored_pages); + count_vm_events(ZSWPOUT, nr_pages); + + ret = true; + +put_pool: + zswap_pool_put(pool); +put_objcg: + obj_cgroup_put(objcg); +reject: + /* + * If the zswap store fails or zswap is disabled, we must invalidate + * the possibly stale entries which were previously stored at the + * offsets corresponding to each page of the folio. Otherwise, + * writeback could overwrite the new data in the swapfile. + */ + if (!ret) { + struct zswap_entry *entry; + long i; + + for (i = 0; i < nr_pages; ++i) { + entry = xa_erase(tree, offset + i); + if (entry) + zswap_entry_free(entry); + } + + if (zswap_pool_reached_full) + queue_work(shrink_wq, &zswap_shrink_work); + } + + return ret; } bool zswap_load(struct folio *folio) -- 2.27.0
