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Date: Sat, 26 Feb 2011 18:58:52 +0800
From: Yongqiang Yang <xiaoqiangnk@...il.com>
To: Andreas Dilger <adilger@...ger.ca>
Cc: linux-ext4@...r.kernel.org
Subject: Re: [PATCH v3] ext4:Make FIEMAP and delayed allocation play well together.
On Sat, Feb 26, 2011 at 4:01 AM, Andreas Dilger <adilger@...ger.ca> wrote:
> On 2011-02-25, at 6:46 AM, Yongqiang Yang wrote:
>> 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?
>
> Yes, as large a file that is possible to keep in DELALLOC state. I think that will require tuning the VM to avoid writeout for as long as possible, and of course making sure that the fiemap tool is not using FIEMAP_FLAG_SYNC:
>
> /proc/sys/vm/dirty_expire_centisecs:60000 # 10 minutes
> /proc/sys/vm/dirty_writeback_centisecs:60000
> /proc/sys/vm/dirty_ratio:99 # 99% of RAM dirty before flush
I used a computer with 4GB memory, and set as you said above. Then, I
dd a 2GB file , fiemap it. However, most of blocks of a file has been
allocated except last 10 thousands ones.
>
> Hopefully this does not lock up your system, so long as the dirty data is kept below the amount of free RAM.
>
>> I think kmalloc() is faster than single-page.
>
> I hope so as well.
>
>> 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
>
>
> Cheers, Andreas
>
>
>
>
>
>
--
Best Wishes
Yongqiang Yang
--
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