On 2020/7/1 9:59, Chao Yu wrote:
> On 2020/7/1 4:56, Jaegeuk Kim wrote:
>> On 06/30, Nathan Chancellor wrote:
>>> On Mon, Jun 29, 2020 at 01:27:20PM -0700, Jaegeuk Kim wrote:
>>>> If two readahead threads having same offset enter in readpages, every read
>>>> IOs are split and issued to the disk which giving lower bandwidth.
>>>>
>>>> This patch tries to avoid redundant readahead calls.
>>>>
>>>> Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org>
>>>> ---
>>>> v3:
>>>> - use READ|WRITE_ONCE
>>>> v2:
>>>> - add missing code to bypass read
>>>>
>>>> fs/f2fs/data.c | 18 ++++++++++++++++++
>>>> fs/f2fs/f2fs.h | 1 +
>>>> fs/f2fs/super.c | 2 ++
>>>> 3 files changed, 21 insertions(+)
>>>>
>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>> index 995cf78b23c5e..360b4c9080d97 100644
>>>> --- a/fs/f2fs/data.c
>>>> +++ b/fs/f2fs/data.c
>>>> @@ -2296,6 +2296,7 @@ static int f2fs_mpage_readpages(struct inode *inode,
>>>> unsigned nr_pages = rac ? readahead_count(rac) : 1;
>>>> unsigned max_nr_pages = nr_pages;
>>>> int ret = 0;
>>>> + bool drop_ra = false;
>>>>
>>>> map.m_pblk = 0;
>>>> map.m_lblk = 0;
>>>> @@ -2306,10 +2307,24 @@ static int f2fs_mpage_readpages(struct inode
>>>> *inode,
>>>> map.m_seg_type = NO_CHECK_TYPE;
>>>> map.m_may_create = false;
>>>>
>>>> + /*
>>>> + * Two readahead threads for same address range can cause race condition
>>>> + * which fragments sequential read IOs. So let's avoid each other.
>>>> + */
>>>> + if (rac && readahead_count(rac)) {
>>>> + if (READ_ONCE(F2FS_I(inode)->ra_offset) == readahead_index(rac))
>>>> + drop_ra = true;
>>>> + else
>>>> + WRITE_ONCE(F2FS_I(inode)->ra_offset,
>>>> + readahead_index(rac));
>>>> + }
>>>> +
>>>> for (; nr_pages; nr_pages--) {
>>>> if (rac) {
>>>> page = readahead_page(rac);
>>>> prefetchw(&page->flags);
>>>> + if (drop_ra)
>>>> + goto next_page;
>>>
>>> When CONFIG_F2FS_FS_COMPRESSION is not set (i.e. x86_64 defconfig +
>>> CONFIG_F2FS_FS=y):
>>>
>>> $ make -skj"$(nproc)" O=out distclean defconfig fs/f2fs/data.o
>>> ../fs/f2fs/data.c: In function ‘f2fs_mpage_readpages’:
>>> ../fs/f2fs/data.c:2327:5: error: label ‘next_page’ used but not defined
>>> 2327 | goto next_page;
>>> | ^~~~
>>> ...
>>
>> Thanks. I pushed the fix for -next.
>> https://lore.kernel.org/linux-f2fs-devel/1be18397-7fc6-703e-121b-e210e1013...@infradead.org/T/#t
It will hang the kernel because we missed to unlock those cached pages,
I changed to 'goto set_error_page', the issue was gone.
Thanks,
>
> Reviewed-by: Chao Yu <yuch...@huawei.com>
>
> Thanks,
>
>>
>> Thanks,
>>
>>>
>>> Cheers,
>>> Nathan
>>>
>>>
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>>
>>
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