From: Vitaly Wool <vitalywool@xxxxxxxxx> Subject: z3fold: add kref refcounting With both coming and already present locking optimizations, introducing kref to reference-count z3fold objects is the right thing to do. Moreover, it makes buddied list no longer necessary, and allows for a simpler handling of headless pages. [akpm@xxxxxxxxxxxxxxxxxxxx: coding-style fixes] Link: http://lkml.kernel.org/r/20170131214650.8ea78033d91ded233f552bc0@xxxxxxxxx Signed-off-by: Vitaly Wool <vitalywool@xxxxxxxxx> Reviewed-by: Dan Streetman <ddstreet@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/z3fold.c | 155 ++++++++++++++++++++++---------------------------- 1 file changed, 69 insertions(+), 86 deletions(-) diff -puN mm/z3fold.c~z3fold-add-kref-refcounting mm/z3fold.c --- a/mm/z3fold.c~z3fold-add-kref-refcounting +++ a/mm/z3fold.c @@ -52,6 +52,7 @@ enum buddy { * z3fold page, except for HEADLESS pages * @buddy: links the z3fold page into the relevant list in the pool * @page_lock: per-page lock + * @refcount: reference cound for the z3fold page * @first_chunks: the size of the first buddy in chunks, 0 if free * @middle_chunks: the size of the middle buddy in chunks, 0 if free * @last_chunks: the size of the last buddy in chunks, 0 if free @@ -60,6 +61,7 @@ enum buddy { struct z3fold_header { struct list_head buddy; spinlock_t page_lock; + struct kref refcount; unsigned short first_chunks; unsigned short middle_chunks; unsigned short last_chunks; @@ -95,8 +97,6 @@ struct z3fold_header { * @unbuddied: array of lists tracking z3fold pages that contain 2- buddies; * the lists each z3fold page is added to depends on the size of * its free region. - * @buddied: list tracking the z3fold pages that contain 3 buddies; - * these z3fold pages are full * @lru: list tracking the z3fold pages in LRU order by most recently * added buddy. * @pages_nr: number of z3fold pages in the pool. @@ -109,7 +109,6 @@ struct z3fold_header { struct z3fold_pool { spinlock_t lock; struct list_head unbuddied[NCHUNKS]; - struct list_head buddied; struct list_head lru; atomic64_t pages_nr; const struct z3fold_ops *ops; @@ -121,8 +120,7 @@ struct z3fold_pool { * Internal z3fold page flags */ enum z3fold_page_flags { - UNDER_RECLAIM = 0, - PAGE_HEADLESS, + PAGE_HEADLESS = 0, MIDDLE_CHUNK_MAPPED, }; @@ -146,11 +144,11 @@ static struct z3fold_header *init_z3fold struct z3fold_header *zhdr = page_address(page); INIT_LIST_HEAD(&page->lru); - clear_bit(UNDER_RECLAIM, &page->private); clear_bit(PAGE_HEADLESS, &page->private); clear_bit(MIDDLE_CHUNK_MAPPED, &page->private); spin_lock_init(&zhdr->page_lock); + kref_init(&zhdr->refcount); zhdr->first_chunks = 0; zhdr->middle_chunks = 0; zhdr->last_chunks = 0; @@ -161,9 +159,24 @@ static struct z3fold_header *init_z3fold } /* Resets the struct page fields and frees the page */ -static void free_z3fold_page(struct z3fold_header *zhdr) +static void free_z3fold_page(struct page *page) { - __free_page(virt_to_page(zhdr)); + __free_page(page); +} + +static void release_z3fold_page(struct kref *ref) +{ + struct z3fold_header *zhdr; + struct page *page; + + zhdr = container_of(ref, struct z3fold_header, refcount); + page = virt_to_page(zhdr); + + if (!list_empty(&zhdr->buddy)) + list_del(&zhdr->buddy); + if (!list_empty(&page->lru)) + list_del(&page->lru); + free_z3fold_page(page); } /* Lock a z3fold page */ @@ -178,7 +191,6 @@ static inline void z3fold_page_unlock(st spin_unlock(&zhdr->page_lock); } - /* * Encodes the handle of a particular buddy within a z3fold page * Pool lock should be held as this function accesses first_num @@ -257,7 +269,6 @@ static struct z3fold_pool *z3fold_create spin_lock_init(&pool->lock); for_each_unbuddied_list(i, 0) INIT_LIST_HEAD(&pool->unbuddied[i]); - INIT_LIST_HEAD(&pool->buddied); INIT_LIST_HEAD(&pool->lru); atomic64_set(&pool->pages_nr, 0); pool->ops = ops; @@ -378,6 +389,7 @@ static int z3fold_alloc(struct z3fold_po spin_unlock(&pool->lock); continue; } + kref_get(&zhdr->refcount); list_del_init(&zhdr->buddy); spin_unlock(&pool->lock); @@ -394,10 +406,12 @@ static int z3fold_alloc(struct z3fold_po else if (zhdr->middle_chunks == 0) bud = MIDDLE; else { + z3fold_page_unlock(zhdr); spin_lock(&pool->lock); - list_add(&zhdr->buddy, &pool->buddied); + if (kref_put(&zhdr->refcount, + release_z3fold_page)) + atomic64_dec(&pool->pages_nr); spin_unlock(&pool->lock); - z3fold_page_unlock(zhdr); pr_err("No free chunks in unbuddied\n"); WARN_ON(1); continue; @@ -438,9 +452,6 @@ found: /* 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); } headless: @@ -504,52 +515,29 @@ static void z3fold_free(struct z3fold_po } } - if (test_bit(UNDER_RECLAIM, &page->private)) { - /* z3fold page is under reclaim, reclaim will free */ - if (bud != HEADLESS) - z3fold_page_unlock(zhdr); - return; - } - - /* Remove from existing buddy list */ - if (bud != HEADLESS) { - spin_lock(&pool->lock); - /* - * this object may have been removed from its list by - * z3fold_alloc(). In that case we just do nothing, - * z3fold_alloc() will allocate an object and add the page - * to the relevant list. - */ - if (!list_empty(&zhdr->buddy)) { - list_del(&zhdr->buddy); - } else { - spin_unlock(&pool->lock); - z3fold_page_unlock(zhdr); - return; - } - spin_unlock(&pool->lock); - } - - if (bud == HEADLESS || - (zhdr->first_chunks == 0 && zhdr->middle_chunks == 0 && - zhdr->last_chunks == 0)) { - /* z3fold page is empty, free */ + if (bud == HEADLESS) { spin_lock(&pool->lock); list_del(&page->lru); spin_unlock(&pool->lock); - clear_bit(PAGE_HEADLESS, &page->private); - if (bud != HEADLESS) - z3fold_page_unlock(zhdr); - free_z3fold_page(zhdr); + free_z3fold_page(page); atomic64_dec(&pool->pages_nr); } else { - z3fold_compact_page(zhdr); - /* Add to the unbuddied list */ + if (zhdr->first_chunks != 0 || zhdr->middle_chunks != 0 || + zhdr->last_chunks != 0) { + z3fold_compact_page(zhdr); + /* Add to the unbuddied list */ + spin_lock(&pool->lock); + if (!list_empty(&zhdr->buddy)) + list_del(&zhdr->buddy); + freechunks = num_free_chunks(zhdr); + list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); + spin_unlock(&pool->lock); + } + z3fold_page_unlock(zhdr); spin_lock(&pool->lock); - freechunks = num_free_chunks(zhdr); - list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); + if (kref_put(&zhdr->refcount, release_z3fold_page)) + atomic64_dec(&pool->pages_nr); spin_unlock(&pool->lock); - z3fold_page_unlock(zhdr); } } @@ -608,13 +596,13 @@ static int z3fold_reclaim_page(struct z3 return -EINVAL; } page = list_last_entry(&pool->lru, struct page, lru); - list_del(&page->lru); + list_del_init(&page->lru); - /* Protect z3fold page against free */ - set_bit(UNDER_RECLAIM, &page->private); zhdr = page_address(page); if (!test_bit(PAGE_HEADLESS, &page->private)) { - list_del(&zhdr->buddy); + if (!list_empty(&zhdr->buddy)) + list_del_init(&zhdr->buddy); + kref_get(&zhdr->refcount); spin_unlock(&pool->lock); z3fold_page_lock(zhdr); /* @@ -655,30 +643,19 @@ static int z3fold_reclaim_page(struct z3 goto next; } next: - if (!test_bit(PAGE_HEADLESS, &page->private)) - z3fold_page_lock(zhdr); - clear_bit(UNDER_RECLAIM, &page->private); - if ((test_bit(PAGE_HEADLESS, &page->private) && ret == 0) || - (zhdr->first_chunks == 0 && zhdr->last_chunks == 0 && - zhdr->middle_chunks == 0)) { - /* - * All buddies are now free, free the z3fold page and - * return success. - */ - if (!test_and_clear_bit(PAGE_HEADLESS, &page->private)) - z3fold_page_unlock(zhdr); - free_z3fold_page(zhdr); - atomic64_dec(&pool->pages_nr); - return 0; - } else if (!test_bit(PAGE_HEADLESS, &page->private)) { - if (zhdr->first_chunks != 0 && - zhdr->last_chunks != 0 && - zhdr->middle_chunks != 0) { - /* Full, add to buddied list */ - spin_lock(&pool->lock); - list_add(&zhdr->buddy, &pool->buddied); - spin_unlock(&pool->lock); + if (test_bit(PAGE_HEADLESS, &page->private)) { + if (ret == 0) { + free_z3fold_page(page); + return 0; } else { + spin_lock(&pool->lock); + } + } else { + z3fold_page_lock(zhdr); + if ((zhdr->first_chunks || zhdr->last_chunks || + zhdr->middle_chunks) && + !(zhdr->first_chunks && zhdr->last_chunks && + zhdr->middle_chunks)) { z3fold_compact_page(zhdr); /* add to unbuddied list */ spin_lock(&pool->lock); @@ -687,13 +664,19 @@ next: &pool->unbuddied[freechunks]); spin_unlock(&pool->lock); } - } - - if (!test_bit(PAGE_HEADLESS, &page->private)) z3fold_page_unlock(zhdr); + spin_lock(&pool->lock); + if (kref_put(&zhdr->refcount, release_z3fold_page)) { + atomic64_dec(&pool->pages_nr); + return 0; + } + } - spin_lock(&pool->lock); - /* add to beginning of LRU */ + /* + * Add to the beginning of LRU. + * Pool lock has to be kept here to ensure the page has + * not already been released + */ list_add(&page->lru, &pool->lru); } spin_unlock(&pool->lock); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
