Messages in this thread | | | Subject | Re: [PATCH v2 RFC] f2fs: fix to force keeping write barrier for strict fsync mode | From | Chao Yu <> | Date | Wed, 14 Jul 2021 10:51:18 +0800 |
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On 2021/7/14 10:19, Jaegeuk Kim wrote: > On 07/14, Chao Yu wrote: >> On 2021/7/14 7:34, Jaegeuk Kim wrote: >>> On 07/13, Chao Yu wrote: >>>> On 2021/7/8 1:48, Jaegeuk Kim wrote: >>>>> On 07/02, Chao Yu wrote: >>>>>> On 2021/7/2 9:32, Jaegeuk Kim wrote: >>>>>>> On 07/02, Chao Yu wrote: >>>>>>>> On 2021/7/2 1:10, Jaegeuk Kim wrote: >>>>>>>>> On 06/01, Chao Yu wrote: >>>>>>>>>> [1] https://www.mail-archive.com/linux-f2fs-devel@lists.sourceforge.net/msg15126.html >>>>>>>>>> >>>>>>>>>> As [1] reported, if lower device doesn't support write barrier, in below >>>>>>>>>> case: >>>>>>>>>> >>>>>>>>>> - write page #0; persist >>>>>>>>>> - overwrite page #0 >>>>>>>>>> - fsync >>>>>>>>>> - write data page #0 OPU into device's cache >>>>>>>>>> - write inode page into device's cache >>>>>>>>>> - issue flush >>>>>>>>> >>>>>>>>> Well, we have preflush for node writes, so I don't think this is the case. >>>>>>>>> >>>>>>>>> fio.op_flags |= REQ_PREFLUSH | REQ_FUA; >>>>>>>> >>>>>>>> This is only used for atomic write case, right? >>>>>>>> >>>>>>>> I mean the common case which is called from f2fs_issue_flush() in >>>>>>>> f2fs_do_sync_file(). >>>>>>> >>>>>>> How about adding PREFLUSH when writing node blocks aligned to the above set? >>>>>> >>>>>> You mean implementation like v1 as below? >>>>>> >>>>>> https://lore.kernel.org/linux-f2fs-devel/20200120100045.70210-1-yuchao0@huawei.com/ >>>>> >>>>> Yea, I think so. :P >>>> >>>> I prefer v2, we may have several schemes to improve performance with v2, e.g. >>>> - use inplace IO to avoid newly added preflush >>>> - use flush_merge option to avoid redundant preflush >>>> - if lower device supports barrier IO, we can avoid newly added preflush >>> >>> Doesn't v2 give one more flush than v1? Why do you want to take worse one and >> >> FUA implies an extra preflush command or similar mechanism in lower device to keep data >> in bio being persistent before this command's completion. >> >> Also if lower device doesn't support FUA natively, block layer turns it into an empty >> PREFLUSH command. >> >> So, it's hard to say which one will win the benchmark game, maybe we need some >> performance data before making the choice, but you know, it depends on device's >> character. > > I was looking at # of bios. > >> >>> try to improve back? Not clear the benefit on v2. >> >> Well, if user suffer and complain performance regression with v1, any plan to improve it? >> >> I just thought about plan B/C/D for no matter v1 or v2. > > I assumed you wanted v2 since it might be used for B/C/D improvements. But, it > seems it wasn't. My point is to save one bio, but piggyback the flag to the > device driver.
I doubt the conclusion...but it needs to get some data to prove it.
I think the right way is merging v1 now to fix the bug firstly, and let me do the comparison on them a little bit later to see whether we need another implementation... thoughts?
Thanks,
> >> >> Thanks, >> >>> >>>> >>>> Thanks, >>>> >>>>> >>>>>> >>>>>> Thanks, >>>>>> >>>>>>> >>>>>>>> >>>>>>>> And please see do_checkpoint(), we call f2fs_flush_device_cache() and >>>>>>>> commit_checkpoint() separately to keep persistence order of CP datas. >>>>>>>> >>>>>>>> See commit 46706d5917f4 ("f2fs: flush cp pack except cp pack 2 page at first") >>>>>>>> for details. >>>>>>>> >>>>>>>> Thanks, >>>>>>>> >>>>>>>>> >>>>>>>>>> >>>>>>>>>> If SPO is triggered during flush command, inode page can be persisted >>>>>>>>>> before data page #0, so that after recovery, inode page can be recovered >>>>>>>>>> with new physical block address of data page #0, however there may >>>>>>>>>> contains dummy data in new physical block address. >>>>>>>>>> >>>>>>>>>> Then what user will see is: after overwrite & fsync + SPO, old data in >>>>>>>>>> file was corrupted, if any user do care about such case, we can suggest >>>>>>>>>> user to use STRICT fsync mode, in this mode, we will force to trigger >>>>>>>>>> preflush command to persist data in device cache in prior to node >>>>>>>>>> writeback, it avoids potential data corruption during fsync(). >>>>>>>>>> >>>>>>>>>> Signed-off-by: Chao Yu <yuchao0@huawei.com> >>>>>>>>>> --- >>>>>>>>>> v2: >>>>>>>>>> - fix this by adding additional preflush command rather than using >>>>>>>>>> atomic write flow. >>>>>>>>>> fs/f2fs/file.c | 14 ++++++++++++++ >>>>>>>>>> 1 file changed, 14 insertions(+) >>>>>>>>>> >>>>>>>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c >>>>>>>>>> index 7d5311d54f63..238ca2a733ac 100644 >>>>>>>>>> --- a/fs/f2fs/file.c >>>>>>>>>> +++ b/fs/f2fs/file.c >>>>>>>>>> @@ -301,6 +301,20 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end, >>>>>>>>>> f2fs_exist_written_data(sbi, ino, UPDATE_INO)) >>>>>>>>>> goto flush_out; >>>>>>>>>> goto out; >>>>>>>>>> + } else { >>>>>>>>>> + /* >>>>>>>>>> + * for OPU case, during fsync(), node can be persisted before >>>>>>>>>> + * data when lower device doesn't support write barrier, result >>>>>>>>>> + * in data corruption after SPO. >>>>>>>>>> + * So for strict fsync mode, force to trigger preflush to keep >>>>>>>>>> + * data/node write order to avoid potential data corruption. >>>>>>>>>> + */ >>>>>>>>>> + if (F2FS_OPTION(sbi).fsync_mode == FSYNC_MODE_STRICT && >>>>>>>>>> + !atomic) { >>>>>>>>>> + ret = f2fs_issue_flush(sbi, inode->i_ino); >>>>>>>>>> + if (ret) >>>>>>>>>> + goto out; >>>>>>>>>> + } >>>>>>>>>> } >>>>>>>>>> go_write: >>>>>>>>>> /* >>>>>>>>>> -- >>>>>>>>>> 2.29.2
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