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This has a number of shortcomings. First, this imposes atomic requirements on compression backends. zram can call both zcomp_compress() and zcomp_decompress() under entry spin-lock, which implies that we can use only compression algorithms that don't schedule/sleep/wait during compression and decompression. This, for instance, makes it impossible to use some of the ASYNC compression algorithms (H/W compression, etc.) implementations. Second, this can potentially trigger watchdogs. For example, entry re-compression with secondary algorithms is performed under entry spin-lock. Given that we chain secondary compression algorithms and that some of them can be configured for best compression ratio (and worst compression speed) zram can stay under spin-lock for quite some time. Do not use per-entry spin-locks and instead convert it to an atomic_t variable which open codes reader-writer type of lock. This permits preemption from slot_lock section, also reduces the sizeof() zram entry when lockdep is enabled. Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zram_drv.c | 126 ++++++++++++++++++++-------------- drivers/block/zram/zram_drv.h | 6 +- 2 files changed, 79 insertions(+), 53 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 9f5020b077c5..1c2df2341704 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -58,19 +58,50 @@ static void zram_free_page(struct zram *zram, size_t in= dex); static int zram_read_from_zspool(struct zram *zram, struct page *page, u32 index); =20 -static int zram_slot_trylock(struct zram *zram, u32 index) +static bool zram_slot_try_write_lock(struct zram *zram, u32 index) { - return spin_trylock(&zram->table[index].lock); + atomic_t *lock =3D &zram->table[index].lock; + int old =3D ZRAM_ENTRY_UNLOCKED; + + return atomic_try_cmpxchg(lock, &old, ZRAM_ENTRY_WRLOCKED); +} + +static void zram_slot_write_lock(struct zram *zram, u32 index) +{ + atomic_t *lock =3D &zram->table[index].lock; + int old =3D atomic_read(lock); + + do { + if (old !=3D ZRAM_ENTRY_UNLOCKED) { + cond_resched(); + old =3D atomic_read(lock); + continue; + } + } while (!atomic_try_cmpxchg(lock, &old, ZRAM_ENTRY_WRLOCKED)); +} + +static void zram_slot_write_unlock(struct zram *zram, u32 index) +{ + atomic_set(&zram->table[index].lock, ZRAM_ENTRY_UNLOCKED); } =20 -static void zram_slot_lock(struct zram *zram, u32 index) +static void zram_slot_read_lock(struct zram *zram, u32 index) { - spin_lock(&zram->table[index].lock); + atomic_t *lock =3D &zram->table[index].lock; + int old =3D atomic_read(lock); + + do { + if (old =3D=3D ZRAM_ENTRY_WRLOCKED) { + cond_resched(); + old =3D atomic_read(lock); + continue; + } + } while (!atomic_try_cmpxchg(lock, &old, old + 1)); } =20 -static void zram_slot_unlock(struct zram *zram, u32 index) +static void zram_slot_read_unlock(struct zram *zram, u32 index) { - spin_unlock(&zram->table[index].lock); + atomic_dec(&zram->table[index].lock); } =20 static inline bool init_done(struct zram *zram) @@ -93,7 +124,6 @@ static void zram_set_handle(struct zram *zram, u32 index= , unsigned long handle) zram->table[index].handle =3D handle; } =20 -/* flag operations require table entry bit_spin_lock() being held */ static bool zram_test_flag(struct zram *zram, u32 index, enum zram_pageflags flag) { @@ -229,9 +259,9 @@ static void release_pp_slot(struct zram *zram, struct z= ram_pp_slot *pps) { list_del_init(&pps->entry); =20 - zram_slot_lock(zram, pps->index); + zram_slot_write_lock(zram, pps->index); zram_clear_flag(zram, pps->index, ZRAM_PP_SLOT); - zram_slot_unlock(zram, pps->index); + zram_slot_write_unlock(zram, pps->index); =20 kfree(pps); } @@ -394,11 +424,11 @@ static void mark_idle(struct zram *zram, ktime_t cuto= ff) * * And ZRAM_WB slots simply cannot be ZRAM_IDLE. */ - zram_slot_lock(zram, index); + zram_slot_write_lock(zram, index); if (!zram_allocated(zram, index) || zram_test_flag(zram, index, ZRAM_WB) || zram_test_flag(zram, index, ZRAM_SAME)) { - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); continue; } =20 @@ -410,7 +440,7 @@ static void mark_idle(struct zram *zram, ktime_t cutoff) zram_set_flag(zram, index, ZRAM_IDLE); else zram_clear_flag(zram, index, ZRAM_IDLE); - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); } } =20 @@ -709,7 +739,7 @@ static int scan_slots_for_writeback(struct zram *zram, = u32 mode, =20 INIT_LIST_HEAD(&pps->entry); =20 - zram_slot_lock(zram, index); + zram_slot_write_lock(zram, index); if (!zram_allocated(zram, index)) goto next; =20 @@ -731,7 +761,7 @@ static int scan_slots_for_writeback(struct zram *zram, = u32 mode, place_pp_slot(zram, ctl, pps); pps =3D NULL; next: - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); } =20 kfree(pps); @@ -822,7 +852,7 @@ static ssize_t writeback_store(struct device *dev, } =20 index =3D pps->index; - zram_slot_lock(zram, index); + zram_slot_read_lock(zram, index); /* * scan_slots() sets ZRAM_PP_SLOT and relases slot lock, so * slots can change in the meantime. If slots are accessed or @@ -833,7 +863,7 @@ static ssize_t writeback_store(struct device *dev, goto next; if (zram_read_from_zspool(zram, page, index)) goto next; - zram_slot_unlock(zram, index); + zram_slot_read_unlock(zram, index); =20 bio_init(&bio, zram->bdev, &bio_vec, 1, REQ_OP_WRITE | REQ_SYNC); @@ -860,7 +890,7 @@ static ssize_t writeback_store(struct device *dev, } =20 atomic64_inc(&zram->stats.bd_writes); - zram_slot_lock(zram, index); + zram_slot_write_lock(zram, index); /* * Same as above, we release slot lock during writeback so * slot can change under us: slot_free() or slot_free() and @@ -882,7 +912,7 @@ static ssize_t writeback_store(struct device *dev, zram->bd_wb_limit -=3D 1UL << (PAGE_SHIFT - 12); spin_unlock(&zram->wb_limit_lock); next: - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); release_pp_slot(zram, pps); =20 cond_resched(); @@ -1001,7 +1031,7 @@ static ssize_t read_block_state(struct file *file, ch= ar __user *buf, for (index =3D *ppos; index < nr_pages; index++) { int copied; =20 - zram_slot_lock(zram, index); + zram_slot_read_lock(zram, index); if (!zram_allocated(zram, index)) goto next; =20 @@ -1019,13 +1049,13 @@ static ssize_t read_block_state(struct file *file, = char __user *buf, ZRAM_INCOMPRESSIBLE) ? 'n' : '.'); =20 if (count <=3D copied) { - zram_slot_unlock(zram, index); + zram_slot_read_unlock(zram, index); break; } written +=3D copied; count -=3D copied; next: - zram_slot_unlock(zram, index); + zram_slot_read_unlock(zram, index); *ppos +=3D 1; } =20 @@ -1473,15 +1503,11 @@ static bool zram_meta_alloc(struct zram *zram, u64 = disksize) huge_class_size =3D zs_huge_class_size(zram->mem_pool); =20 for (index =3D 0; index < num_pages; index++) - spin_lock_init(&zram->table[index].lock); + atomic_set(&zram->table[index].lock, ZRAM_ENTRY_UNLOCKED); + return true; } =20 -/* - * To protect concurrent access to the same index entry, - * caller should hold this table index entry's bit_spinlock to - * indicate this index entry is accessing. - */ static void zram_free_page(struct zram *zram, size_t index) { unsigned long handle; @@ -1602,17 +1628,17 @@ static int zram_read_page(struct zram *zram, struct= page *page, u32 index, { int ret; =20 - zram_slot_lock(zram, index); + zram_slot_read_lock(zram, index); if (!zram_test_flag(zram, index, ZRAM_WB)) { /* Slot should be locked through out the function call */ ret =3D zram_read_from_zspool(zram, page, index); - zram_slot_unlock(zram, index); + zram_slot_read_unlock(zram, index); } else { /* * The slot should be unlocked before reading from the backing * device. */ - zram_slot_unlock(zram, index); + zram_slot_read_unlock(zram, index); =20 ret =3D read_from_bdev(zram, page, zram_get_handle(zram, index), parent); @@ -1655,10 +1681,10 @@ static int zram_bvec_read(struct zram *zram, struct= bio_vec *bvec, static int write_same_filled_page(struct zram *zram, unsigned long fill, u32 index) { - zram_slot_lock(zram, index); + zram_slot_write_lock(zram, index); zram_set_flag(zram, index, ZRAM_SAME); zram_set_handle(zram, index, fill); - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); =20 atomic64_inc(&zram->stats.same_pages); atomic64_inc(&zram->stats.pages_stored); @@ -1693,11 +1719,11 @@ static int write_incompressible_page(struct zram *z= ram, struct page *page, kunmap_local(src); zs_unmap_object(zram->mem_pool, handle); =20 - zram_slot_lock(zram, index); + zram_slot_write_lock(zram, index); zram_set_flag(zram, index, ZRAM_HUGE); zram_set_handle(zram, index, handle); zram_set_obj_size(zram, index, PAGE_SIZE); - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); =20 atomic64_add(PAGE_SIZE, &zram->stats.compr_data_size); atomic64_inc(&zram->stats.huge_pages); @@ -1718,9 +1744,9 @@ static int zram_write_page(struct zram *zram, struct = page *page, u32 index) bool same_filled; =20 /* First, free memory allocated to this slot (if any) */ - zram_slot_lock(zram, index); + zram_slot_write_lock(zram, index); zram_free_page(zram, index); - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); =20 mem =3D kmap_local_page(page); same_filled =3D page_same_filled(mem, &element); @@ -1790,10 +1816,10 @@ static int zram_write_page(struct zram *zram, struc= t page *page, u32 index) zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]); zs_unmap_object(zram->mem_pool, handle); =20 - zram_slot_lock(zram, index); + zram_slot_write_lock(zram, index); zram_set_handle(zram, index, handle); zram_set_obj_size(zram, index, comp_len); - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); =20 /* Update stats */ atomic64_inc(&zram->stats.pages_stored); @@ -1850,7 +1876,7 @@ static int scan_slots_for_recompress(struct zram *zra= m, u32 mode, =20 INIT_LIST_HEAD(&pps->entry); =20 - zram_slot_lock(zram, index); + zram_slot_write_lock(zram, index); if (!zram_allocated(zram, index)) goto next; =20 @@ -1871,7 +1897,7 @@ static int scan_slots_for_recompress(struct zram *zra= m, u32 mode, place_pp_slot(zram, ctl, pps); pps =3D NULL; next: - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); } =20 kfree(pps); @@ -2162,7 +2188,7 @@ static ssize_t recompress_store(struct device *dev, if (!num_recomp_pages) break; =20 - zram_slot_lock(zram, pps->index); + zram_slot_write_lock(zram, pps->index); if (!zram_test_flag(zram, pps->index, ZRAM_PP_SLOT)) goto next; =20 @@ -2170,7 +2196,7 @@ static ssize_t recompress_store(struct device *dev, &num_recomp_pages, threshold, prio, prio_max); next: - zram_slot_unlock(zram, pps->index); + zram_slot_write_unlock(zram, pps->index); release_pp_slot(zram, pps); =20 if (err) { @@ -2217,9 +2243,9 @@ static void zram_bio_discard(struct zram *zram, struc= t bio *bio) } =20 while (n >=3D PAGE_SIZE) { - zram_slot_lock(zram, index); + zram_slot_write_lock(zram, index); zram_free_page(zram, index); - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); atomic64_inc(&zram->stats.notify_free); index++; n -=3D PAGE_SIZE; @@ -2248,9 +2274,9 @@ static void zram_bio_read(struct zram *zram, struct b= io *bio) } flush_dcache_page(bv.bv_page); =20 - zram_slot_lock(zram, index); + zram_slot_write_lock(zram, index); zram_accessed(zram, index); - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); =20 bio_advance_iter_single(bio, &iter, bv.bv_len); } while (iter.bi_size); @@ -2278,9 +2304,9 @@ static void zram_bio_write(struct zram *zram, struct = bio *bio) break; } =20 - zram_slot_lock(zram, index); + zram_slot_write_lock(zram, index); zram_accessed(zram, index); - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); =20 bio_advance_iter_single(bio, &iter, bv.bv_len); } while (iter.bi_size); @@ -2321,13 +2347,13 @@ static void zram_slot_free_notify(struct block_devi= ce *bdev, zram =3D bdev->bd_disk->private_data; =20 atomic64_inc(&zram->stats.notify_free); - if (!zram_slot_trylock(zram, index)) { + if (!zram_slot_try_write_lock(zram, index)) { atomic64_inc(&zram->stats.miss_free); return; } =20 zram_free_page(zram, index); - zram_slot_unlock(zram, index); + zram_slot_write_unlock(zram, index); } =20 static void zram_comp_params_reset(struct zram *zram) diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h index db78d7c01b9a..e20538cdf565 100644 --- a/drivers/block/zram/zram_drv.h +++ b/drivers/block/zram/zram_drv.h @@ -28,7 +28,6 @@ #define ZRAM_SECTOR_PER_LOGICAL_BLOCK \ (1 << (ZRAM_LOGICAL_BLOCK_SHIFT - SECTOR_SHIFT)) =20 - /* * ZRAM is mainly used for memory efficiency so we want to keep memory * footprint small and thus squeeze size and zram pageflags into a flags @@ -58,13 +57,14 @@ enum zram_pageflags { __NR_ZRAM_PAGEFLAGS, }; =20 -/*-- Data structures */ +#define ZRAM_ENTRY_UNLOCKED 0 +#define ZRAM_ENTRY_WRLOCKED (-1) =20 /* Allocated for each disk page */ struct zram_table_entry { unsigned long handle; unsigned int flags; - spinlock_t lock; + atomic_t lock; #ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME ktime_t ac_time; #endif --=20 2.48.1.362.g079036d154-goog