Re: [PATCH v6] iomap: support tail packing inline read

Huang Jianan
2021-07-23T06:22:57Z

Hi Xiang,

I have tested this patch based on the erofs dax support below, It works
well for me.

https://git.kernel.org/pub/scm/linux/kernel/git/xiang/linux.git/log/?h=erofs/dax

Tested-by: Huang Jianan <huangjianan@oppo.com>

Thanks,

Jianan

On 2021/7/23 9:26, Gao Xiang wrote:
> Hi Darrick,
>
> On Thu, Jul 22, 2021 at 09:51:09AM -0700, Darrick J. Wong wrote:
>> On Thu, Jul 22, 2021 at 07:39:47AM +0200, Christoph Hellwig wrote:
>>> I think some of the language here is confusing - mostly about tail
>>> packing when we otherwise use inline data. Can you take a look at
>>> the version below? This mostly cleans up the terminology, adds a
>>> new helper to check the size, and removes the error on trying to
>>> write with a non-zero pos, as it can be trivially supported now.
>>>
>>> ---
>>> From 0f9c6ac6c2e372739b29195d25bebb8dd87e583a Mon Sep 17 00:00:00 2001
>>> From: Gao Xiang <hsiangkao@linux.alibaba.com>
>>> Date: Thu, 22 Jul 2021 11:17:29 +0800
>>> Subject: iomap: make inline data support more flexible
>>>
>>> Add support for offsets into the inline data page at iomap->inline_data
>>> to cater for the EROFS tailpackng case where a small data is stored
>>> right after the inode.
>> The commit message is a little misleading -- this adds support for
>> inline data pages at nonzero (but page-aligned) file offsets, not file
>> offsets into the page itself. I suggest:
>>
>> "Add support for reading inline data content into the page cache from
>> nonzero page-aligned file offsets. This enables the EROFS tailpacking
>> mode where the last few bytes of the file are stored right after the
>> inode."
>>
>> The code changes look good to me.
> Thanks for your suggestion. I've tested EROFS with no problem so far.
>
> I could update the commit message like this, what should I do next?
>
> Many thanks,
> Gao Xiang
>
>> --D
>>
>>> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
>>> ---
>>> fs/iomap/buffered-io.c | 35 ++++++++++++++++++-----------------
>>> fs/iomap/direct-io.c | 10 ++++++----
>>> include/linux/iomap.h | 14 ++++++++++++++
>>> 3 files changed, 38 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
>>> index 87ccb3438becd9..0597f5c186a33f 100644
>>> --- a/fs/iomap/buffered-io.c
>>> +++ b/fs/iomap/buffered-io.c
>>> @@ -205,25 +205,29 @@ struct iomap_readpage_ctx {
>>> struct readahead_control *rac;
>>> };
>>>
>>> -static void
>>> -iomap_read_inline_data(struct inode *inode, struct page *page,
>>> - struct iomap *iomap)
>>> +static int iomap_read_inline_data(struct inode *inode, struct page *page,
>>> + struct iomap *iomap, loff_t pos)
>>> {
>>> - size_t size = i_size_read(inode);
>>> + size_t size = iomap->length + iomap->offset - pos;
>>> void *addr;
>>>
>>> if (PageUptodate(page))
>>> - return;
>>> + return PAGE_SIZE;
>>>
>>> - BUG_ON(page_has_private(page));
>>> - BUG_ON(page->index);
>>> - BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
>>> + /* inline data must start page aligned in the file */
>>> + if (WARN_ON_ONCE(offset_in_page(pos)))
>>> + return -EIO;
>>> + if (WARN_ON_ONCE(!iomap_inline_data_size_valid(iomap)))
>>> + return -EIO;
>>> + if (WARN_ON_ONCE(page_has_private(page)))
>>> + return -EIO;
>>>
>>> addr = kmap_atomic(page);
>>> - memcpy(addr, iomap->inline_data, size);
>>> + memcpy(addr, iomap_inline_buf(iomap, pos), size);
>>> memset(addr + size, 0, PAGE_SIZE - size);
>>> kunmap_atomic(addr);
>>> SetPageUptodate(page);
>>> + return PAGE_SIZE;
>>> }
>>>
>>> static inline bool iomap_block_needs_zeroing(struct inode *inode,
>>> @@ -246,11 +250,8 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>>> unsigned poff, plen;
>>> sector_t sector;
>>>
>>> - if (iomap->type == IOMAP_INLINE) {
>>> - WARN_ON_ONCE(pos);
>>> - iomap_read_inline_data(inode, page, iomap);
>>> - return PAGE_SIZE;
>>> - }
>>> + if (iomap->type == IOMAP_INLINE)
>>> + return iomap_read_inline_data(inode, page, iomap, pos);
>>>
>>> /* zero post-eof blocks as the page may be mapped */
>>> iop = iomap_page_create(inode, page);
>>> @@ -618,14 +619,14 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
>>> }
>>>
>>> if (srcmap->type == IOMAP_INLINE)
>>> - iomap_read_inline_data(inode, page, srcmap);
>>> + status = iomap_read_inline_data(inode, page, srcmap, pos);
>>> else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
>>> status = __block_write_begin_int(page, pos, len, NULL, srcmap);
>>> else
>>> status = __iomap_write_begin(inode, pos, len, flags, page,
>>> srcmap);
>>>
>>> - if (unlikely(status))
>>> + if (unlikely(status < 0))
>>> goto out_unlock;
>>>
>>> *pagep = page;
>>> @@ -675,7 +676,7 @@ static size_t iomap_write_end_inline(struct inode *inode, struct page *page,
>>>
>>> flush_dcache_page(page);
>>> addr = kmap_atomic(page);
>>> - memcpy(iomap->inline_data + pos, addr + pos, copied);
>>> + memcpy(iomap_inline_buf(iomap, pos), addr + pos, copied);
>>> kunmap_atomic(addr);
>>>
>>> mark_inode_dirty(inode);
>>> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
>>> index 9398b8c31323b3..a6aaea2764a55f 100644
>>> --- a/fs/iomap/direct-io.c
>>> +++ b/fs/iomap/direct-io.c
>>> @@ -378,23 +378,25 @@ iomap_dio_inline_actor(struct inode *inode, loff_t pos, loff_t length,
>>> struct iomap_dio *dio, struct iomap *iomap)
>>> {
>>> struct iov_iter *iter = dio->submit.iter;
>>> + void *dst = iomap_inline_buf(iomap, pos);
>>> size_t copied;
>>>
>>> - BUG_ON(pos + length > PAGE_SIZE - offset_in_page(iomap->inline_data));
>>> + if (WARN_ON_ONCE(!iomap_inline_data_size_valid(iomap)))
>>> + return -EIO;
>>>
>>> if (dio->flags & IOMAP_DIO_WRITE) {
>>> loff_t size = inode->i_size;
>>>
>>> if (pos > size)
>>> - memset(iomap->inline_data + size, 0, pos - size);
>>> - copied = copy_from_iter(iomap->inline_data + pos, length, iter);
>>> + memset(iomap_inline_buf(iomap, size), 0, pos - size);
>>> + copied = copy_from_iter(dst, length, iter);
>>> if (copied) {
>>> if (pos + copied > size)
>>> i_size_write(inode, pos + copied);
>>> mark_inode_dirty(inode);
>>> }
>>> } else {
>>> - copied = copy_to_iter(iomap->inline_data + pos, length, iter);
>>> + copied = copy_to_iter(dst, length, iter);
>>> }
>>> dio->size += copied;
>>> return copied;
>>> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
>>> index 479c1da3e2211e..5efae7153912ed 100644
>>> --- a/include/linux/iomap.h
>>> +++ b/include/linux/iomap.h
>>> @@ -97,6 +97,20 @@ iomap_sector(struct iomap *iomap, loff_t pos)
>>> return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT;
>>> }
>>>
>>> +static inline void *iomap_inline_buf(const struct iomap *iomap, loff_t pos)
>>> +{
>>> + return iomap->inline_data - iomap->offset + pos;
>>> +}
>>> +
>>> +/*
>>> + * iomap->inline_data is a potentially kmapped page, ensure it never crosseѕ a
>>> + * page boundary.
>>> + */
>>> +static inline bool iomap_inline_data_size_valid(const struct iomap *iomap)
>>> +{
>>> + return iomap->length <= PAGE_SIZE - offset_in_page(iomap->inline_data);
>>> +}
>>> +
>>> /*
>>> * When a filesystem sets page_ops in an iomap mapping it returns, page_prepare
>>> * and page_done will be called for each page written to. This only applies to
>>> --
>>> 2.30.2
>>>