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

[Nitin Gupta <ngupta@vflare.org>]

On 01/20/2013 09:18 PM, Minchan Kim wrote:
> 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.
>

I meant to check if we can get rid of zram_meta entirely, by open coding 
zram_meta_alloc in disksize_store itself. But looks like that will be 
very error prone with so many goto's.

Otherwise, I prefer struct zram->meta declaration, as is done in this 
patch, instead of duplicating those four fields in both struct zram and 
struct zram_meta and there's no point worrying about that extra dereference.

Thanks,
Nitin


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