Re: [PATCH] Squashfs: add asynchronous read support
From: Minchan Kim
Date: Tue Dec 17 2013 - 02:27:07 EST
Hello Chanho,
On Mon, Dec 16, 2013 at 02:30:26PM +0900, Chanho Min wrote:
> This patch removes synchronous wait for the up-to-date of buffer in the
> file system level. Instead all operations after submit_bh are moved into
> the End-of-IO handler and its associated workeque. It decompresses/copies
> data into pages and unlock them asynchronously.
>
> This patch enhances the performance of Squashfs in most cases.
> Especially, large file reading is improved significantly.
>
> dd read test:
>
> - ARM cortex-a9 1GHz, 2 cores, eMMC 4.5 HS200 mode.
> - dd if=file1 of=/dev/null bs=64k
>
> Before
> 58707718 bytes (56.0MB) copied, 1.393653 seconds, 40.2MB/s
>
> After
> 58707718 bytes (56.0MB) copied, 0.942413 seconds, 59.4MB/s
It's really nice!
I did test it on x86 with USB stick and ARM with eMMC on my Nexus 4.
In experiment, I couldn't see much gain like you both system and
even it was regressed at bs=32k test, maybe workqueue
allocation/schedule of work per I/O.
Your test is rather special or what I am missing?
Before that, I'd like to know fundamental reason why your implementation
for asynchronous read enhance. At a first glance, I thought it's caused
by readahead from MM layer but when I read code, I found I was wrong.
MM's readahead logic works based on PageReadahead marker but squashfs
invalidates by grab_cache_page_nowait so it wouldn't work as we expected.
Another possibility is block I/O merging in block layder by plugging logic,
which was what I tried a few month ago although implementation was really
bad. But it wouldn't work with your patch because do_generic_file_read
will unplug block layer by lock_page without merging enough I/O.
So, what do you think real actuator for enhance your experiment?
Then, I could investigate why I can't get a benefit.
Thanks for looking this.
>
> Signed-off-by: Chanho Min <chanho.min@xxxxxxx>
> ---
> fs/squashfs/Kconfig | 9 ++
> fs/squashfs/block.c | 262 +++++++++++++++++++++++++++++++++++++++++++++
> fs/squashfs/file_direct.c | 8 +-
> fs/squashfs/page_actor.c | 3 +-
> fs/squashfs/page_actor.h | 3 +-
> fs/squashfs/squashfs.h | 2 +
> 6 files changed, 284 insertions(+), 3 deletions(-)
>
> diff --git a/fs/squashfs/Kconfig b/fs/squashfs/Kconfig
> index b6fa865..284aa5a 100644
> --- a/fs/squashfs/Kconfig
> +++ b/fs/squashfs/Kconfig
> @@ -51,6 +51,15 @@ config SQUASHFS_FILE_DIRECT
> it eliminates a memcpy and it also removes the lock contention
> on the single buffer.
>
> +config SQUASHFS_READ_DATA_ASYNC
> + bool "Read and decompress data asynchronously"
> + depends on SQUASHFS_FILE_DIRECT
> + help
> + By default Squashfs read data synchronously by block (default 128k).
> + This option removes such a synchronous wait in the file system level.
> + All works after submit IO do at the End-of-IO handler asynchronously.
> + This enhances the performance of Squashfs in most cases, especially,
> + large file reading.
> endchoice
>
> choice
> diff --git a/fs/squashfs/block.c b/fs/squashfs/block.c
> index 0cea9b9..1517ca3 100644
> --- a/fs/squashfs/block.c
> +++ b/fs/squashfs/block.c
> @@ -212,3 +212,265 @@ read_failure:
> kfree(bh);
> return -EIO;
> }
> +
> +#ifdef CONFIG_SQUASHFS_READ_DATA_ASYNC
> +
> +struct squashfs_end_io_assoc {
> + int offset;
> + int b_count;
> + int compressed;
> + int length;
> + struct squashfs_page_actor *p_actor;
> + struct buffer_head **__bh;
> + struct squashfs_sb_info *msblk;
> + struct work_struct read_work;
> +};
> +
> +static int squashfs_copy_page(struct squashfs_sb_info *msblk,
> + struct buffer_head **bh, int b, int offset, int length,
> + struct squashfs_page_actor *output)
> +{
> + /*
> + * Block is uncompressed.
> + */
> + int in, pg_offset = 0, avail = 0, bytes, k = 0;
> + void *data = squashfs_first_page(output);
> + for (bytes = length; k < b; k++) {
> + in = min(bytes, msblk->devblksize - offset);
> + bytes -= in;
> + while (in) {
> + if (pg_offset == PAGE_CACHE_SIZE) {
> + data = squashfs_next_page(output);
> + pg_offset = 0;
> + }
> + avail = min_t(int, in, PAGE_CACHE_SIZE -
> + pg_offset);
> + memcpy(data + pg_offset, bh[k]->b_data + offset,
> + avail);
> + in -= avail;
> + pg_offset += avail;
> + offset += avail;
> + }
> + offset = 0;
> + put_bh(bh[k]);
> + }
> + squashfs_finish_page(output);
> + return length;
> +}
> +
> +/*
> + * This is executed in workqueue for squashfs_read_data_async().
> + * - pages come decompressed/copied and unlocked asynchronously.
> + */
> +static void squashfs_buffer_read_async(struct squashfs_end_io_assoc *io_assoc)
> +{
> + struct squashfs_sb_info *msblk = io_assoc->msblk;
> + struct squashfs_page_actor *actor = io_assoc->p_actor;
> + struct page **page = actor->page;
> + int pages = actor->pages;
> + struct page *target_page = actor->target_page;
> + int i, length, bytes = 0;
> + void *pageaddr;
> +
> + if (io_assoc->compressed) {
> + length = squashfs_decompress(msblk, io_assoc->__bh,
> + io_assoc->b_count, io_assoc->offset,
> + io_assoc->length, actor);
> + if (length < 0) {
> + ERROR("squashfs_read_data failed to read block\n");
> + goto read_failure;
> + }
> + } else
> + length = squashfs_copy_page(msblk, io_assoc->__bh,
> + io_assoc->b_count, io_assoc->offset,
> + io_assoc->length, actor);
> +
> + /* Last page may have trailing bytes not filled */
> + bytes = length % PAGE_CACHE_SIZE;
> + if (bytes) {
> + pageaddr = kmap_atomic(page[pages - 1]);
> + memset(pageaddr + bytes, 0, PAGE_CACHE_SIZE - bytes);
> + kunmap_atomic(pageaddr);
> + }
> +
> + /* Mark pages as uptodate, unlock and release */
> + for (i = 0; i < pages; i++) {
> + flush_dcache_page(page[i]);
> + SetPageUptodate(page[i]);
> + unlock_page(page[i]);
> + if (page[i] != target_page)
> + page_cache_release(page[i]);
> + }
> +
> + kfree(io_assoc->__bh);
> + kfree(actor);
> + kfree(page);
> + kfree(io_assoc);
> + return;
> +
> +read_failure:
> + /* Decompression failed, mark pages as errored. Target_page is
> + * dealt with by the caller
> + */
> + for (i = 0; i < pages; i++) {
> + if (page[i] == NULL || page[i] == target_page)
> + continue;
> + flush_dcache_page(page[i]);
> + SetPageError(page[i]);
> + unlock_page(page[i]);
> + page_cache_release(page[i]);
> + }
> +
> + kfree(io_assoc->__bh);
> + kfree(actor);
> + kfree(page);
> + kfree(io_assoc);
> + return;
> +}
> +
> +static void squashfs_async_work(struct work_struct *work)
> +{
> + struct squashfs_end_io_assoc *io_assoc =
> + container_of(work, struct squashfs_end_io_assoc, read_work);
> +
> + squashfs_buffer_read_async(io_assoc);
> +}
> +
> +/*
> + * squashfs_buffer_end_io: update buffer and check if all buffers of array
> + * are updated then invoke the wq for async read.
> + */
> +static void squashfs_buffer_end_io(struct buffer_head *bh, int uptodate)
> +{
> + int i;
> + struct squashfs_end_io_assoc *io_assoc = bh->b_private;
> +
> + if (uptodate) {
> + set_buffer_uptodate(bh);
> + } else {
> + /* This happens, due to failed READA attempts. */
> + clear_buffer_uptodate(bh);
> + }
> + unlock_buffer(bh);
> + put_bh(bh);
> +
> + BUG_ON(!io_assoc);
> +
> + /* Check if all buffers are uptodate */
> + for (i = 0; i < io_assoc->b_count; i++)
> + if (!buffer_uptodate(io_assoc->__bh[i]))
> + return;
> +
> + schedule_work(&io_assoc->read_work);
> +}
> +
> +/*
> + * squashfs_ll_r_block: low-level access to block devices for squashfs.
> + * @nr: number of &struct buffer_heads in the array
> + * @bhs: array of pointers to &struct buffer_head
> + *
> + * squashfs_ll_r_block sets b_end_io to the squashfs specific completion handler
> + * that marks the buffer up-to-date and invokes workqueue for decompression
> + * and uptodate of pages if needed.
> + */
> +static void squashfs_ll_r_block(int nr, struct buffer_head *bhs[])
> +{
> + int i, s_nr = 0;
> + struct squashfs_end_io_assoc *io_assoc = NULL;
> +
> + for (i = 0; i < nr; i++) {
> + struct buffer_head *bh = bhs[i];
> + io_assoc = bh->b_private;
> + if (!trylock_buffer(bh))
> + continue;
> + if (!buffer_uptodate(bh)) {
> + bh->b_end_io = squashfs_buffer_end_io;
> + get_bh(bh);
> + s_nr++;
> + submit_bh(READ, bh);
> + continue;
> + }
> + unlock_buffer(bh);
> + }
> + /*
> + * All buffers are uptodate, but no submit_bh is occurred.
> + * Then try to unlock pages directly.
> + */
> + if (nr && !s_nr && io_assoc)
> + squashfs_buffer_read_async(io_assoc);
> +}
> +
> +/*
> + * Read and datablock asynchronously. same as squashfs_read_data(),
> + * except it doesn't block until a buffer comes unlocked.
> + * the work after submit IO do at the End-Of-Handle and the associated wq.
> + */
> +int squashfs_read_data_async(struct super_block *sb, u64 index, int length,
> + struct squashfs_page_actor *output)
> +{
> + struct squashfs_sb_info *msblk = sb->s_fs_info;
> + struct buffer_head **bh;
> + int offset = index & ((1 << msblk->devblksize_log2) - 1);
> + u64 cur_index = index >> msblk->devblksize_log2;
> + int bytes, compressed, b = 0, k = 0;
> + struct squashfs_end_io_assoc *io_assoc;
> +
> + bh = kcalloc(((output->length + msblk->devblksize - 1)
> + >> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL);
> + if (bh == NULL)
> + return -ENOMEM;
> +
> + if (!length)
> + return -EINVAL;
> +
> + bytes = -offset;
> +
> + compressed = SQUASHFS_COMPRESSED_BLOCK(length);
> + length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
> +
> + TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
> + index, compressed ? "" : "un", length, output->length);
> +
> + if (length < 0 || length > output->length ||
> + (index + length) > msblk->bytes_used)
> + goto read_failure;
> +
> + io_assoc = kmalloc(sizeof(struct squashfs_end_io_assoc), GFP_KERNEL);
> + if (io_assoc == NULL)
> + return -ENOMEM;
> +
> + io_assoc->offset = offset;
> + io_assoc->p_actor = output;
> + io_assoc->compressed = compressed;
> + io_assoc->__bh = bh;
> + io_assoc->length = length;
> + io_assoc->msblk = msblk;
> +
> + INIT_WORK(&io_assoc->read_work, squashfs_async_work);
> +
> + for (b = 0; bytes < length; b++, cur_index++) {
> + bh[b] = sb_getblk(sb, cur_index);
> + if (bh[b] == NULL)
> + goto block_release;
> + bytes += msblk->devblksize;
> + if (!buffer_locked(bh[b]))
> + bh[b]->b_private = io_assoc;
> + }
> + io_assoc->b_count = b;
> +
> + /* make sure io_assoc is updated before submit IO */
> + mb();
> + squashfs_ll_r_block(b, bh);
> + return length;
> +
> +block_release:
> + for (; k < b; k++)
> + put_bh(bh[k]);
> +
> +read_failure:
> + ERROR("squashfs_read_data failed to read block 0x%llx\n",
> + (unsigned long long) index);
> + kfree(bh);
> + return -EIO;
> +}
> +#endif
> diff --git a/fs/squashfs/file_direct.c b/fs/squashfs/file_direct.c
> index 62a0de6..610ca17 100644
> --- a/fs/squashfs/file_direct.c
> +++ b/fs/squashfs/file_direct.c
> @@ -52,7 +52,7 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
> * Create a "page actor" which will kmap and kunmap the
> * page cache pages appropriately within the decompressor
> */
> - actor = squashfs_page_actor_init_special(page, pages, 0);
> + actor = squashfs_page_actor_init_special(page, pages, target_page, 0);
> if (actor == NULL)
> goto out;
>
> @@ -91,6 +91,11 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
> }
>
> /* Decompress directly into the page cache buffers */
> +#ifdef CONFIG_SQUASHFS_READ_DATA_ASYNC
> + squashfs_read_data_async(inode->i_sb, block, bsize, actor);
> +
> + return 0;
> +#else
> res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
> if (res < 0)
> goto mark_errored;
> @@ -116,6 +121,7 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
> kfree(page);
>
> return 0;
> +#endif
>
> mark_errored:
> /* Decompression failed, mark pages as errored. Target_page is
> diff --git a/fs/squashfs/page_actor.c b/fs/squashfs/page_actor.c
> index 5a1c11f..2d2d7ac 100644
> --- a/fs/squashfs/page_actor.c
> +++ b/fs/squashfs/page_actor.c
> @@ -81,7 +81,7 @@ static void direct_finish_page(struct squashfs_page_actor *actor)
> }
>
> struct squashfs_page_actor *squashfs_page_actor_init_special(struct page **page,
> - int pages, int length)
> + int pages, struct page *target_page, int length)
> {
> struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
>
> @@ -91,6 +91,7 @@ struct squashfs_page_actor *squashfs_page_actor_init_special(struct page **page,
> actor->length = length ? : pages * PAGE_CACHE_SIZE;
> actor->page = page;
> actor->pages = pages;
> + actor->target_page = target_page;
> actor->next_page = 0;
> actor->pageaddr = NULL;
> actor->squashfs_first_page = direct_first_page;
> diff --git a/fs/squashfs/page_actor.h b/fs/squashfs/page_actor.h
> index 26dd820..b50d982 100644
> --- a/fs/squashfs/page_actor.h
> +++ b/fs/squashfs/page_actor.h
> @@ -58,13 +58,14 @@ struct squashfs_page_actor {
> void *(*squashfs_next_page)(struct squashfs_page_actor *);
> void (*squashfs_finish_page)(struct squashfs_page_actor *);
> int pages;
> + struct page *target_page;
> int length;
> int next_page;
> };
>
> extern struct squashfs_page_actor *squashfs_page_actor_init(void **, int, int);
> extern struct squashfs_page_actor *squashfs_page_actor_init_special(struct page
> - **, int, int);
> + **, int, struct page *, int);
> static inline void *squashfs_first_page(struct squashfs_page_actor *actor)
> {
> return actor->squashfs_first_page(actor);
> diff --git a/fs/squashfs/squashfs.h b/fs/squashfs/squashfs.h
> index 9e1bb79..39e95af 100644
> --- a/fs/squashfs/squashfs.h
> +++ b/fs/squashfs/squashfs.h
> @@ -30,6 +30,8 @@
> /* block.c */
> extern int squashfs_read_data(struct super_block *, u64, int, u64 *,
> struct squashfs_page_actor *);
> +extern int squashfs_read_data_async(struct super_block *, u64, int,
> + struct squashfs_page_actor *);
>
> /* cache.c */
> extern struct squashfs_cache *squashfs_cache_init(char *, int, int);
> --
> 1.7.9.5
>
> --
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--
Kind regards,
Minchan Kim
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