On 2019/7/1 18:13, Andreas Grünbacher wrote:
> Am Mo., 1. Juli 2019 um 12:09 Uhr schrieb Chao Yu <yuchao0@xxxxxxxxxx>:
>> On 2019/7/1 17:49, Andreas Grünbacher wrote:
>>> Am Mo., 1. Juli 2019 um 10:04 Uhr schrieb Gao Xiang <gaoxiang25@xxxxxxxxxx>:
>>>> On 2019/7/1 14:40, Chao Yu wrote:
>>>>> Hi Xiang,
>>>>>
>>>>> On 2019/6/29 17:34, Gao Xiang wrote:
>>>>>> Hi Chao,
>>>>>>
>>>>>> On 2019/6/29 15:30, Chao Yu wrote:
>>>>>>> Some filesystems like erofs/reiserfs have the ability to pack tail
>>>>>>> data into metadata, however iomap framework can only support mapping
>>>>>>> inline data with IOMAP_INLINE type, it restricts that:
>>>>>>> - inline data should be locating at page #0.
>>>>>>> - inline size should equal to .i_size
>>>>>>> So we can not use IOMAP_INLINE to handle tail-packing case.
>>>>>>>
>>>>>>> This patch introduces new mapping type IOMAP_TAIL to map tail-packed
>>>>>>> data for further use of erofs.
>>>>>>>
>>>>>>> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
>>>>>>> ---
>>>>>>> fs/iomap.c | 22 ++++++++++++++++++++++
>>>>>>> include/linux/iomap.h | 1 +
>>>>>>> 2 files changed, 23 insertions(+)
>>>>>>>
>>>>>>> diff --git a/fs/iomap.c b/fs/iomap.c
>>>>>>> index 12654c2e78f8..ae7777ce77d0 100644
>>>>>>> --- a/fs/iomap.c
>>>>>>> +++ b/fs/iomap.c
>>>>>>> @@ -280,6 +280,23 @@ iomap_read_inline_data(struct inode *inode, struct page *page,
>>>>>>> SetPageUptodate(page);
>>>>>>> }
>>>>>>>
>>>>>>> +static void
>>>>>>> +iomap_read_tail_data(struct inode *inode, struct page *page,
>>>>>>> + struct iomap *iomap)
>>>>>>> +{
>>>>>>> + size_t size = i_size_read(inode) & (PAGE_SIZE - 1);
>>>>>>> + void *addr;
>>>>>>> +
>>>>>>> + if (PageUptodate(page))
>>>>>>> + return;
>>>>>>> +
>>>>>>> + addr = kmap_atomic(page);
>>>>>>> + memcpy(addr, iomap->inline_data, size);
>>>>>>> + memset(addr + size, 0, PAGE_SIZE - size);
>>>>>>
>>>>>> need flush_dcache_page(page) here for new page cache page since
>>>>>> it's generic iomap code (althrough not necessary for x86, arm), I am not sure...
>>>>>> see commit d2b2c6dd227b and c01778001a4f...
>>>>>
>>>>> Thanks for your reminding, these all codes were copied from
>>>>> iomap_read_inline_data(), so I think we need a separated patch to fix this issue
>>>>> if necessary.
>>>>
>>>> Yes, just a reminder, it is good as it-is.
>>>
>>> Not sure if that means that IOMAP_INLINE as is works for you now. In
>>> any case, if the inline data isn't transparently copied into the page
>>> cache at index 0, memory-mapped I/O isn't going to work.
>>>
>>> The code further assumes that "packed" files consist of exactly one
>>> IOMAP_INLINE mapping; no IOMAP_MAPPED or other mappings may follow. Is
>>> it that assumption that's causing you trouble? If so, what's the
>>
>> Yes, that's the problem we met.
>>
>>> layout at the filesystem level you want to support?
>>
>> The layout which can support tail-merge one, it means if the data locating at
>> the tail of file has small enough size, we can inline the tail data into
>> metadata area. e.g.:
>>
>> IOMAP_MAPPED [0, 8192]
>> IOMAP_INLINE (or maybe IOMAP_TAIL) [8192, 8200]
>
> Ah, now I see. Let's generalize the IOMAP_INLINE code to support that
> and rename it to IOMAP_TAIL then.
Okay, it's fine to me, let me refactor the RFC patch. ;)
Thanks,
>
> Thanks,
> Andreas
> .
>
