Re: [PATCH 3/3] zram: get rid of lockdep warning

Minchan Kim
2013-01-21T05:18:47Z

On Fri, Jan 18, 2013 at 01:34:18PM -0800, Nitin Gupta wrote:
> On Wed, Jan 16, 2013 at 6:12 PM, Minchan Kim <minchan@kernel.org> wrote:
> > Lockdep complains about recursive deadlock of zram->init_lock.
> > [1] made it false positive because we can't request IO to zram
> > before setting disksize. Anyway, we should shut lockdep up to
> > avoid many reporting from user.
> >
> > This patch allocates zram's metadata out of lock so we can fix it.
> > In addition, this patch replace GFP_KERNEL with GFP_NOIO/GFP_ATOMIC
> > in request handle path for partial I/O.
> >
> > [1] zram: give up lazy initialization of zram metadata
> >
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> > drivers/staging/zram/zram_drv.c | 194 +++++++++++++++++++------------------
> > drivers/staging/zram/zram_drv.h | 12 ++-
> > drivers/staging/zram/zram_sysfs.c | 13 ++-
> > 3 files changed, 118 insertions(+), 101 deletions(-)
> >
> > diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> > index 3693780..eb1bc37 100644
> > --- a/drivers/staging/zram/zram_drv.c
> > +++ b/drivers/staging/zram/zram_drv.c
> > @@ -71,22 +71,22 @@ static void zram_stat64_inc(struct zram *zram, u64 *v)
> > zram_stat64_add(zram, v, 1);
> > }
> >
> > -static int zram_test_flag(struct zram *zram, u32 index,
> > +static int zram_test_flag(struct zram_meta *meta, u32 index,
> > enum zram_pageflags flag)
> > {
> > - return zram->table[index].flags & BIT(flag);
> > + return meta->table[index].flags & BIT(flag);
> > }
> >
> > -static void zram_set_flag(struct zram *zram, u32 index,
> > +static void zram_set_flag(struct zram_meta *meta, u32 index,
> > enum zram_pageflags flag)
> > {
> > - zram->table[index].flags |= BIT(flag);
> > + meta->table[index].flags |= BIT(flag);
> > }
> >
> > -static void zram_clear_flag(struct zram *zram, u32 index,
> > +static void zram_clear_flag(struct zram_meta *meta, u32 index,
> > enum zram_pageflags flag)
> > {
> > - zram->table[index].flags &= ~BIT(flag);
> > + meta->table[index].flags &= ~BIT(flag);
> > }
> >
> > static int page_zero_filled(void *ptr)
> > @@ -106,16 +106,17 @@ static int page_zero_filled(void *ptr)
> >
> > static void zram_free_page(struct zram *zram, size_t index)
> > {
> > - unsigned long handle = zram->table[index].handle;
> > - u16 size = zram->table[index].size;
> > + struct zram_meta *meta = zram->meta;
> > + unsigned long handle = meta->table[index].handle;
> > + u16 size = meta->table[index].size;
> >
> > if (unlikely(!handle)) {
> > /*
> > * No memory is allocated for zero filled pages.
> > * Simply clear zero page flag.
> > */
> > - if (zram_test_flag(zram, index, ZRAM_ZERO)) {
> > - zram_clear_flag(zram, index, ZRAM_ZERO);
> > + if (zram_test_flag(meta, index, ZRAM_ZERO)) {
> > + zram_clear_flag(meta, index, ZRAM_ZERO);
> > zram_stat_dec(&zram->stats.pages_zero);
> > }
> > return;
> > @@ -124,17 +125,17 @@ static void zram_free_page(struct zram *zram, size_t index)
> > if (unlikely(size > max_zpage_size))
> > zram_stat_dec(&zram->stats.bad_compress);
> >
> > - zs_free(zram->mem_pool, handle);
> > + zs_free(meta->mem_pool, handle);
> >
> > if (size <= PAGE_SIZE / 2)
> > zram_stat_dec(&zram->stats.good_compress);
> >
> > zram_stat64_sub(zram, &zram->stats.compr_size,
> > - zram->table[index].size);
> > + meta->table[index].size);
> > zram_stat_dec(&zram->stats.pages_stored);
> >
> > - zram->table[index].handle = 0;
> > - zram->table[index].size = 0;
> > + meta->table[index].handle = 0;
> > + meta->table[index].size = 0;
> > }
> >
> > static void handle_zero_page(struct bio_vec *bvec)
> > @@ -159,20 +160,21 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
> > int ret = LZO_E_OK;
> > size_t clen = PAGE_SIZE;
> > unsigned char *cmem;
> > - unsigned long handle = zram->table[index].handle;
> > + struct zram_meta *meta = zram->meta;
> > + unsigned long handle = meta->table[index].handle;
> >
> > - if (!handle || zram_test_flag(zram, index, ZRAM_ZERO)) {
> > + if (!handle || zram_test_flag(meta, index, ZRAM_ZERO)) {
> > memset(mem, 0, PAGE_SIZE);
> > return 0;
> > }
> >
> > - cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
> > - if (zram->table[index].size == PAGE_SIZE)
> > + cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_RO);
> > + if (meta->table[index].size == PAGE_SIZE)
> > memcpy(mem, cmem, PAGE_SIZE);
> > else
> > - ret = lzo1x_decompress_safe(cmem, zram->table[index].size,
> > + ret = lzo1x_decompress_safe(cmem, meta->table[index].size,
> > mem, &clen);
> > - zs_unmap_object(zram->mem_pool, handle);
> > + zs_unmap_object(meta->mem_pool, handle);
> >
> > /* Should NEVER happen. Return bio error if it does. */
> > if (unlikely(ret != LZO_E_OK)) {
> > @@ -190,11 +192,11 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
> > int ret;
> > struct page *page;
> > unsigned char *user_mem, *uncmem = NULL;
> > -
> > + struct zram_meta *meta = zram->meta;
> > page = bvec->bv_page;
> >
> > - if (unlikely(!zram->table[index].handle) ||
> > - zram_test_flag(zram, index, ZRAM_ZERO)) {
> > + if (unlikely(!meta->table[index].handle) ||
> > + zram_test_flag(meta, index, ZRAM_ZERO)) {
> > handle_zero_page(bvec);
> > return 0;
> > }
> > @@ -202,7 +204,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
> > user_mem = kmap_atomic(page);
> > if (is_partial_io(bvec))
> > /* Use a temporary buffer to decompress the page */
> > - uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> > + uncmem = kmalloc(PAGE_SIZE, GFP_ATOMIC);
> > else
> > uncmem = user_mem;
> >
> > @@ -241,16 +243,17 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> > unsigned long handle;
> > struct page *page;
> > unsigned char *user_mem, *cmem, *src, *uncmem = NULL;
> > + struct zram_meta *meta = zram->meta;
> >
> > page = bvec->bv_page;
> > - src = zram->compress_buffer;
> > + src = meta->compress_buffer;
> >
> > if (is_partial_io(bvec)) {
> > /*
> > * This is a partial IO. We need to read the full page
> > * before to write the changes.
> > */
> > - uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> > + uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
> > if (!uncmem) {
> > pr_info("Error allocating temp memory!\n");
> > ret = -ENOMEM;
> > @@ -265,8 +268,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> > * System overwrites unused sectors. Free memory associated
> > * with this sector now.
> > */
> > - if (zram->table[index].handle ||
> > - zram_test_flag(zram, index, ZRAM_ZERO))
> > + if (meta->table[index].handle ||
> > + zram_test_flag(meta, index, ZRAM_ZERO))
> > zram_free_page(zram, index);
> >
> > user_mem = kmap_atomic(page);
> > @@ -284,13 +287,13 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> > if (!is_partial_io(bvec))
> > kunmap_atomic(user_mem);
> > zram_stat_inc(&zram->stats.pages_zero);
> > - zram_set_flag(zram, index, ZRAM_ZERO);
> > + zram_set_flag(meta, index, ZRAM_ZERO);
> > ret = 0;
> > goto out;
> > }
> >
> > ret = lzo1x_1_compress(uncmem, PAGE_SIZE, src, &clen,
> > - zram->compress_workmem);
> > + meta->compress_workmem);
> >
> > if (!is_partial_io(bvec)) {
> > kunmap_atomic(user_mem);
> > @@ -311,14 +314,14 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> > src = uncmem;
> > }
> >
> > - handle = zs_malloc(zram->mem_pool, clen);
> > + handle = zs_malloc(meta->mem_pool, clen);
> > if (!handle) {
> > pr_info("Error allocating memory for compressed "
> > "page: %u, size=%zu\n", index, clen);
> > ret = -ENOMEM;
> > goto out;
> > }
> > - cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
> > + cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_WO);
> >
> > if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
> > src = kmap_atomic(page);
> > @@ -326,10 +329,10 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> > if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
> > kunmap_atomic(src);
> >
> > - zs_unmap_object(zram->mem_pool, handle);
> > + zs_unmap_object(meta->mem_pool, handle);
> >
> > - zram->table[index].handle = handle;
> > - zram->table[index].size = clen;
> > + meta->table[index].handle = handle;
> > + meta->table[index].size = clen;
> >
> > /* Update stats */
> > zram_stat64_add(zram, &zram->stats.compr_size, clen);
> > @@ -472,33 +475,24 @@ error:
> > void __zram_reset_device(struct zram *zram)
> > {
> > size_t index;
> > + struct zram_meta *meta;
> >
> > if (!zram->init_done)
> > goto out;
> >
> > + meta = zram->meta;
> > zram->init_done = 0;
> > -
> > - /* Free various per-device buffers */
> > - kfree(zram->compress_workmem);
> > - free_pages((unsigned long)zram->compress_buffer, 1);
> > -
> > - zram->compress_workmem = NULL;
> > - zram->compress_buffer = NULL;
> > -
> > /* Free all pages that are still in this zram device */
> > for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
> > - unsigned long handle = zram->table[index].handle;
> > + unsigned long handle = meta->table[index].handle;
> > if (!handle)
> > continue;
> >
> > - zs_free(zram->mem_pool, handle);
> > + zs_free(meta->mem_pool, handle);
> > }
> >
> > - vfree(zram->table);
> > - zram->table = NULL;
> > -
> > - zs_destroy_pool(zram->mem_pool);
> > - zram->mem_pool = NULL;
> > + zram_meta_free(zram->meta);
> > + zram->meta = NULL;
> >
> > /* Reset stats */
> > memset(&zram->stats, 0, sizeof(zram->stats));
> > @@ -514,12 +508,64 @@ void zram_reset_device(struct zram *zram)
> > up_write(&zram->init_lock);
> > }
> >
> > -/* zram->init_lock should be held */
> > -int zram_init_device(struct zram *zram)
> > +void zram_meta_free(struct zram_meta *meta)
> > {
> > - int ret;
> > - size_t num_pages;
> > + zs_destroy_pool(meta->mem_pool);
> > + kfree(meta->compress_workmem);
> > + free_pages((unsigned long)meta->compress_buffer, 1);
> > + vfree(meta->table);
> > + kfree(meta);
> > +}
> > +
> > +struct zram_meta *zram_meta_alloc(u64 disksize)
> > +{
> > + size_t num_pages;
> > + struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
> > + if (!meta)
> > + goto out;
> > +
> > + meta->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
> > + if (!meta->compress_workmem) {
> > + pr_err("Error allocating compressor working memory!\n");
> > + goto free_meta;
> > + }
> > +
> > + meta->compress_buffer = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
> > + if (!meta->compress_buffer) {
> > + pr_err("Error allocating compressor buffer space\n");
> > + goto free_workmem;
> > + }
> > +
> > + num_pages = disksize >> PAGE_SHIFT;
> > + meta->table = vzalloc(num_pages * sizeof(*meta->table));
> > + if (!meta->table) {
> > + pr_err("Error allocating zram address table\n");
> > + goto free_buffer;
> > + }
> > +
> > + meta->mem_pool = zs_create_pool("zram", GFP_NOIO | __GFP_HIGHMEM);
> > + if (!meta->mem_pool) {
> > + pr_err("Error creating memory pool\n");
> > + goto free_table;
> > + }
> > +
> > + return meta;
> > +
> > +free_table:
> > + vfree(meta->table);
> > +free_buffer:
> > + free_pages((unsigned long)meta->compress_buffer, 1);
> > +free_workmem:
> > + kfree(meta->compress_workmem);
> > +free_meta:
> > + kfree(meta);
> > + meta = NULL;
> > +out:
> > + return meta;
> > +}
> >
> > +void zram_init_device(struct zram *zram, struct zram_meta *meta)
> > +{
> > if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
> > pr_info(
> > "There is little point creating a zram of greater than "
> > @@ -534,51 +580,13 @@ int zram_init_device(struct zram *zram)
> > );
> > }
> >
> > - zram->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
> > - if (!zram->compress_workmem) {
> > - pr_err("Error allocating compressor working memory!\n");
> > - ret = -ENOMEM;
> > - goto fail_no_table;
> > - }
> > -
> > - zram->compress_buffer =
> > - (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
> > - if (!zram->compress_buffer) {
> > - pr_err("Error allocating compressor buffer space\n");
> > - ret = -ENOMEM;
> > - goto fail_no_table;
> > - }
> > -
> > - num_pages = zram->disksize >> PAGE_SHIFT;
> > - zram->table = vzalloc(num_pages * sizeof(*zram->table));
> > - if (!zram->table) {
> > - pr_err("Error allocating zram address table\n");
> > - ret = -ENOMEM;
> > - goto fail_no_table;
> > - }
> > -
> > /* zram devices sort of resembles non-rotational disks */
> > queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
> >
> > - zram->mem_pool = zs_create_pool("zram", GFP_NOIO | __GFP_HIGHMEM);
> > - if (!zram->mem_pool) {
> > - pr_err("Error creating memory pool\n");
> > - ret = -ENOMEM;
> > - goto fail;
> > - }
> > -
> > + zram->meta = meta;
> > zram->init_done = 1;
> >
> > pr_debug("Initialization done!\n");
> > - return 0;
> > -
> > -fail_no_table:
> > - /* To prevent accessing table entries during cleanup */
> > - zram->disksize = 0;
> > -fail:
> > - __zram_reset_device(zram);
> > - pr_err("Initialization failed: err=%d\n", ret);
> > - return ret;
> > }
> >
> > static void zram_slot_free_notify(struct block_device *bdev,
> > diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
> > index 5b671d1..2d1a3f1 100644
> > --- a/drivers/staging/zram/zram_drv.h
> > +++ b/drivers/staging/zram/zram_drv.h
> > @@ -83,11 +83,15 @@ struct zram_stats {
> > u32 bad_compress; /* % of pages with compression ratio>=75% */
> > };
> >
> > -struct zram {
> > - struct zs_pool *mem_pool;
> > +struct zram_meta {
> > void *compress_workmem;
> > void *compress_buffer;
> > struct table *table;
> > + struct zs_pool *mem_pool;
> > +};
> > +
> > +struct zram {
> > + struct zram_meta *meta;
> > spinlock_t stat64_lock; /* protect 64-bit stats */
> > struct rw_semaphore lock; /* protect compression buffers and table
> > * against concurrent read and writes */
> > @@ -111,7 +115,9 @@ unsigned int zram_get_num_devices(void);
> > extern struct attribute_group zram_disk_attr_group;
> > #endif
> >
> > -extern int zram_init_device(struct zram *zram);
> > extern void zram_reset_device(struct zram *zram);
> > +extern struct zram_meta *zram_meta_alloc(u64 disksize);
> > +extern void zram_meta_free(struct zram_meta *meta);
> > +extern void zram_init_device(struct zram *zram, struct zram_meta *meta);
> >
>
> This separation of zram and zram_meta looks weird and unncessary. I
> would prefer just having
> a single struct zram as before.

Separation would make code very simple but I admit it has unnecessary
allo/free overhead of zram_meta and dereferencing in hot path.
So I removed it in hotpath but keep it in slow path to make code simple.

Thanks for the review, Nitin!

>
>
> Thanks,
> Nitin
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: email@kvack.org

--
Kind regards,
Minchan Kim