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

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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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >  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
> 
> --
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> see: http://www.linux-mm.org/ .
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-- 
Kind regards,
Minchan Kim

--
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