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Date: Fri, 25 Feb 2011 21:46:31 +0800
From: Yongqiang Yang <xiaoqiangnk@...il.com>
To: Andreas Dilger <adilger@...ger.ca>
Cc: linux-ext4@...r.kernel.org, sandeen@...hat.com
Subject: Re: [PATCH v3] ext4:Make FIEMAP and delayed allocation play well together.
On Fri, Feb 25, 2011 at 6:13 PM, Andreas Dilger <adilger@...ger.ca> wrote:
> On 2011-02-25, at 2:40 AM, Yongqiang Yang wrote:
>> @@ -3782,38 +3783,124 @@ static int ext4_ext_fiemap_cb(struct inode *inode,
>> if (newex->ec_start == 0) {
>> + struct page *page = NULL;
>> +repeat:
>> + last_offset = offset;
>> + head = NULL;
>> + ret = find_get_pages_tag(inode->i_mapping, &offset,
>> + PAGECACHE_TAG_DIRTY, 1, &page);
>
> Hmm, now I wonder about the expense of mapping many thousands of delalloc
> pages, one at a time, in order to map this extent.
>
> Could you please do a test, with as large a file as possible before it is written to disk (say 4GB == 1M pages), to see whether single-page find_get_pages_tag() is faster than kmalloc() of a PAGE_SIZE buffer and (PAGE_SIZE/sizeof(struct page *)) page pointers?
Sorry, my machine's memory is in 2GB size. Should I do a test with a
file in 1.5GB size?
I think kmalloc() is faster than single-page.
Thank you.
>
> This would probably work best if the VM is tuned not to flush out dirty pages.
>
> Otherwise, there are only minor style issues to fix up. Thanks for your work so far.
>
>> + if (!(flags & FIEMAP_EXTENT_DELALLOC)) {
>> + /* First time, try to find a mapped buffer. */
>> + if (ret == 0) {
>> +out:
>> + if (ret > 0)
>> + page_cache_release(page);
>> + /* just a hole. */
>> + return EXT_CONTINUE;
>> + }
>>
>> - if (!bh)
>> - return EXT_CONTINUE;
>> + /* Try to find the 1st mapped buffer. */
>> + end = ((__u64)page->index << PAGE_SHIFT)
>> + >> blksize_bits;
>
> (style) operators go at the end of the previous line.
>
>> + if (!page_has_buffers(page))
>> + goto out;
>> + head = page_buffers(page);
>> + if (!head)
>> + goto out;
>>
>> - if (buffer_delay(bh)) {
>> - flags |= FIEMAP_EXTENT_DELALLOC;
>> - page_cache_release(page);
>> + bh = head;
>> + do {
>> + if (buffer_mapped(bh)) {
>> + /* get the 1st mapped buffer. */
>> + if (end > newex->ec_block +
>> + newex->ec_len)
>
> (style) continued lines should align by the parenthesis '(' on the previous line, not on a full tab.
>
>> + /* The buffer is out of
>> + * the request range.
>> + */
>> + goto out;
>> + goto found_mapped_buffer;
>> + }
>> + bh = bh->b_this_page;
>> + end++;
>> + } while (bh != head);
>> + /* No mapped buffer found. */
>> + goto out;
>> } else {
>> + /*Find contiguous delayed buffers. */
>> + if (ret > 0 && page->index == last_offset)
>> + head = page_buffers(page);
>> + bh = head;
>> + }
>> +
>> +found_mapped_buffer:
>> + if (bh != NULL && buffer_delay(bh)) {
>> + /* 1st or contiguous delayed buffer found. */
>> + if (!(flags & FIEMAP_EXTENT_DELALLOC)) {
>> + /*
>> + * 1st delayed buffer found, record
>> + * the start of extent.
>> + */
>> + flags |= FIEMAP_EXTENT_DELALLOC;
>> + newex->ec_block = end;
>> + logical = (__u64)end << blksize_bits;
>
> (style) remove double space before '('
>
>> + }
>> + /* Find contiguous delayed buffers. */
>> + do {
>> + if (!buffer_delay(bh))
>> + goto found_delayed_extent;
>> + bh = bh->b_this_page;
>> + end++;
>> + } while (bh != head);
>> + } else if (!(flags & FIEMAP_EXTENT_DELALLOC))
>> + /* a hole found. */
>> + goto out;
>> +
>> +found_delayed_extent:
>> + newex->ec_len = min(end - newex->ec_block,
>> + (ext4_lblk_t)EXT_INIT_MAX_LEN);
>
> (style) align continued line after '(' on previous line
>
>> + if (ret == 1 && bh != NULL
>> + && newex->ec_len < EXT_INIT_MAX_LEN
>> + && buffer_delay(bh)) {
>
> (style) operators go at the end of the previous line, like:
>
> + if (ret == 1 && bh != NULL &&
> + newex->ec_len < EXT_INIT_MAX_LEN && buffer_delay(bh)) {
>
>> + /* Have not collected an extent and continue. */
>> page_cache_release(page);
>> - return EXT_CONTINUE;
>> + goto repeat;
>> }
>> + page_cache_release(page);
>> }
>>
>> physical = (__u64)newex->ec_start << blksize_bits;
>> @@ -3822,32 +3909,16 @@ static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path,
>> if (ex && ext4_ext_is_uninitialized(ex))
>> flags |= FIEMAP_EXTENT_UNWRITTEN;
>>
>> - /*
>> - * If this extent reaches EXT_MAX_BLOCK, it must be last.
>> - *
>> - * Or if ext4_ext_next_allocated_block is EXT_MAX_BLOCK,
>> - * this also indicates no more allocated blocks.
>> - *
>> - * XXX this might miss a single-block extent at EXT_MAX_BLOCK
>> - */
>> - if (ext4_ext_next_allocated_block(path) == EXT_MAX_BLOCK ||
>> - newex->ec_block + newex->ec_len - 1 == EXT_MAX_BLOCK) {
>> - loff_t size = i_size_read(inode);
>> - loff_t bs = EXT4_BLOCK_SIZE(inode->i_sb);
>> -
>> + size = i_size_read(inode);
>> + if (logical + length >= size)
>> flags |= FIEMAP_EXTENT_LAST;
>> - if ((flags & FIEMAP_EXTENT_DELALLOC) &&
>> - logical+length > size)
>> - length = (size - logical + bs - 1) & ~(bs-1);
>> - }
>>
>> - error = fiemap_fill_next_extent(fieinfo, logical, physical,
>> + ret = fiemap_fill_next_extent(fieinfo, logical, physical,
>> length, flags);
>> - if (error < 0)
>> - return error;
>> - if (error == 1)
>> + if (ret < 0)
>> + return ret;
>> + if (ret == 1)
>> return EXT_BREAK;
>> -
>> return EXT_CONTINUE;
>> }
>>
>> --
>> 1.7.4
>>
>
>
> Cheers, Andreas
>
>
>
>
>
>
--
Best Wishes
Yongqiang Yang
--
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