On Fri, Aug 30, 2024 at 5:27 AM Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx> wrote: > > zswap_store() will now process and store mTHP and PMD-size THP folios. > > A new config variable CONFIG_ZSWAP_STORE_THP_DEFAULT_ON (off by default) > will enable/disable zswap storing of (m)THP. > > 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 > > This patch provides a sequential implementation of storing an mTHP 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. > > If an error is encountered during the store of any page in the mTHP, > all previous pages/entries stored will be invalidated. Thus, an mTHP > is either entirely stored in ZSWAP, or entirely not stored in ZSWAP. > > This forms the basis for building batching of pages during zswap store > of large folios, by compressing batches of up to say, 8 pages in an > mTHP in parallel in hardware, with the Intel In-Memory Analytics > Accelerator (Intel IAA). Hi Kanchana, I'm not opposed to this patch, but I don't understand how iterating through each page within an mTHP supports the use of Intel IAA, as it involves compressing pages individually. In the document 'by_n compression and decompression with Intel IAA' by Andre Glover (https://lore.kernel.org/all/cover.1714581792.git.andre.glover@xxxxxxxxxxxxxxx), it appears that zsmalloc/zram needs to support multi-page compression and decompression to fully leverage the hardware's capabilities. Could you clarify how this approach fits in? In patch2/3 of that series, you have: "Add the 'by_n' attribute to the acomp_req. The 'by_n' attribute can be used a directive by acomp crypto algorithms for splitting compress and decompress operations into "n" separate jobs." How can you apply 'by_n' to a single page rather than to a large folio? > > Also, addressed some of the RFC comments from the discussion in [1]. > > Made a minor edit in the comments for "struct zswap_entry" to delete > the comments related to "value" since same-filled page handling has > been removed from zswap. > > Co-developed-by: Ryan Roberts > Signed-off-by: > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx> > --- > mm/Kconfig | 8 ++ > mm/zswap.c | 243 +++++++++++++++++++++++++++++++++++++++-------------- > 2 files changed, 190 insertions(+), 61 deletions(-) > > diff --git a/mm/Kconfig b/mm/Kconfig > index b23913d4e47e..68c7b01120bd 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -59,6 +59,14 @@ config ZSWAP_SHRINKER_DEFAULT_ON > reducing the chance that cold pages will reside in the zswap pool > and consume memory indefinitely. > > +config ZSWAP_STORE_THP_DEFAULT_ON > + bool "Store mTHP and THP folios in zswap" > + depends on ZSWAP > + default n > + help > + If selected, zswap will process mTHP and THP folios by > + compressing and storing each 4K page in the large folio. > + > choice > prompt "Default compressor" > depends on ZSWAP > diff --git a/mm/zswap.c b/mm/zswap.c > index 449914ea9919..3abf9810f0b7 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -127,6 +127,14 @@ static bool zswap_shrinker_enabled = IS_ENABLED( > CONFIG_ZSWAP_SHRINKER_DEFAULT_ON); > module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644); > > +/* > + * Enable/disable zswap processing of mTHP folios. > + * For now, only zswap_store will process mTHP folios. > + */ > +static bool zswap_mthp_enabled = IS_ENABLED( > + CONFIG_ZSWAP_STORE_THP_DEFAULT_ON); > +module_param_named(mthp_enabled, zswap_mthp_enabled, bool, 0644); > + > bool zswap_is_enabled(void) > { > return zswap_enabled; > @@ -190,7 +198,6 @@ static struct shrinker *zswap_shrinker; > * section for context. > * pool - the zswap_pool the entry's data is in > * handle - zpool allocation handle that stores the compressed page data > - * value - value of the same-value filled pages which have same content > * objcg - the obj_cgroup that the compressed memory is charged to > * lru - handle to the pool's lru used to evict pages. > */ > @@ -876,7 +883,7 @@ static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node) > return 0; > } > > -static bool zswap_compress(struct folio *folio, struct zswap_entry *entry) > +static bool zswap_compress(struct page *page, struct zswap_entry *entry) > { > struct crypto_acomp_ctx *acomp_ctx; > struct scatterlist input, output; > @@ -894,7 +901,7 @@ static bool zswap_compress(struct folio *folio, struct zswap_entry *entry) > > dst = acomp_ctx->buffer; > sg_init_table(&input, 1); > - sg_set_folio(&input, folio, PAGE_SIZE, 0); > + sg_set_page(&input, page, PAGE_SIZE, 0); > > /* > * We need PAGE_SIZE * 2 here since there maybe over-compression case, > @@ -1404,35 +1411,82 @@ static void shrink_worker(struct work_struct *w) > /********************************* > * main API > **********************************/ > -bool zswap_store(struct folio *folio) > + > +/* > + * Returns true if the entry was successfully > + * stored in the xarray, and false otherwise. > + */ > +static bool zswap_store_entry(struct xarray *tree, > + struct zswap_entry *entry) > { > - swp_entry_t swp = folio->swap; > - pgoff_t offset = swp_offset(swp); > - struct xarray *tree = swap_zswap_tree(swp); > - struct zswap_entry *entry, *old; > - struct obj_cgroup *objcg = NULL; > - struct mem_cgroup *memcg = NULL; > + struct zswap_entry *old; > + pgoff_t offset = swp_offset(entry->swpentry); > > - VM_WARN_ON_ONCE(!folio_test_locked(folio)); > - VM_WARN_ON_ONCE(!folio_test_swapcache(folio)); > + old = xa_store(tree, offset, entry, GFP_KERNEL); > > - /* Large folios aren't supported */ > - if (folio_test_large(folio)) > + if (xa_is_err(old)) { > + int err = xa_err(old); > + > + WARN_ONCE(err != -ENOMEM, "unexpected xarray error: %d\n", err); > + zswap_reject_alloc_fail++; > return false; > + } > > - if (!zswap_enabled) > - goto check_old; > + /* > + * We may have had an existing entry that became stale when > + * the folio was redirtied and now the new version is being > + * swapped out. Get rid of the old. > + */ > + if (old) > + zswap_entry_free(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); > + return true; > +} > + > +/* > + * 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. > + * > + * This is called after the store of the i-th offset in a large folio has > + * failed. All zswap entries in the folio must be deleted. This helps make > + * sure that a swapped-out mTHP is either entirely stored in zswap, or > + * entirely not stored in zswap. > + * > + * This is also called if zswap_store() is invoked, but zswap is not enabled. > + * All offsets for the folio are deleted from zswap in this case. > + */ > +static void zswap_delete_stored_offsets(struct xarray *tree, > + pgoff_t offset, > + long nr_pages) > +{ > + 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); > } > +} > + > +/* > + * Stores the page at specified "index" in a folio. > + */ > +static bool zswap_store_page(struct folio *folio, long index, > + struct obj_cgroup *objcg, > + struct zswap_pool *pool) > +{ > + swp_entry_t swp = folio->swap; > + int type = swp_type(swp); > + pgoff_t offset = swp_offset(swp) + index; > + struct page *page = folio_page(folio, index); > + struct xarray *tree = swap_zswap_tree(swp); > + struct zswap_entry *entry; > + > + if (objcg) > + obj_cgroup_get(objcg); > > if (zswap_check_limits()) > goto reject; > @@ -1445,42 +1499,20 @@ bool zswap_store(struct folio *folio) > } > > /* if entry is successfully added, it keeps the reference */ > - entry->pool = zswap_pool_current_get(); > - if (!entry->pool) > + if (!zswap_pool_get(pool)) > goto freepage; > > - 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, entry)) > + if (!zswap_compress(page, entry)) > goto put_pool; > > - entry->swpentry = swp; > + entry->swpentry = swp_entry(type, offset); > entry->objcg = objcg; > entry->referenced = true; > > - old = xa_store(tree, offset, entry, GFP_KERNEL); > - if (xa_is_err(old)) { > - int err = xa_err(old); > - > - WARN_ONCE(err != -ENOMEM, "unexpected xarray error: %d\n", err); > - zswap_reject_alloc_fail++; > + if (!zswap_store_entry(tree, entry)) > goto store_failed; > - } > - > - /* > - * We may have had an existing entry that became stale when > - * the folio was redirtied and now the new version is being > - * swapped out. Get rid of the old. > - */ > - if (old) > - zswap_entry_free(old); > > if (objcg) { > obj_cgroup_charge_zswap(objcg, entry->length); > @@ -1511,23 +1543,112 @@ bool zswap_store(struct folio *folio) > store_failed: > zpool_free(entry->pool->zpool, entry->handle); > put_pool: > - zswap_pool_put(entry->pool); > + zswap_pool_put(pool); > freepage: > 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; > +} > + > +/* > + * Modified to store mTHP folios. Each page in the mTHP will be compressed > + * and stored sequentially. > + */ > +bool zswap_store(struct folio *folio) > +{ > + long nr_pages = folio_nr_pages(folio); > + swp_entry_t swp = folio->swap; > + pgoff_t offset = swp_offset(swp); > + struct xarray *tree = swap_zswap_tree(swp); > + struct obj_cgroup *objcg = NULL; > + struct mem_cgroup *memcg = NULL; > + struct zswap_pool *pool; > + bool ret = false; > + long index; > + > + VM_WARN_ON_ONCE(!folio_test_locked(folio)); > + VM_WARN_ON_ONCE(!folio_test_swapcache(folio)); > + > + /* Storing large folios isn't enabled */ > + if (!zswap_mthp_enabled && folio_test_large(folio)) > + return false; > + > + 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 limits: > + * > + * The cgroup zswap limit check is done once at the beginning of an > + * mTHP store, and not within zswap_store_page() for each page > + * in the mTHP. We do however check the zswap pool limits at the > + * start of zswap_store_page(). What this means is, the cgroup > + * could go over the limits by at most (HPAGE_PMD_NR - 1) pages. > + * However, the per-store-page zswap pool limits check should > + * hopefully trigger the cgroup aware and zswap LRU aware global > + * reclaim implemented in the shrinker. If this assumption holds, > + * the cgroup exceeding the zswap limits could potentially be > + * resolved before the next zswap_store, and if it is not, the next > + * zswap_store would fail the cgroup zswap limit check at the start. > */ > - 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); > + } > + > + 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 removing all the previous pages we stored. > + */ > + for (index = 0; index < nr_pages; ++index) { > + if (!zswap_store_page(folio, index, objcg, pool)) > + goto put_pool; > + } > + > + ret = true; > + > +put_pool: > + zswap_pool_put(pool); > +put_objcg: > + obj_cgroup_put(objcg); > + if (zswap_pool_reached_full) > + queue_work(shrink_wq, &zswap_shrink_work); > +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) > + zswap_delete_stored_offsets(tree, offset, nr_pages); > + > + return ret; > } > > bool zswap_load(struct folio *folio) > -- > 2.27.0 > Thanks Barry
