Messages in this thread | | | Date | Mon, 19 Jul 2021 11:38:48 -0700 | From | Jaegeuk Kim <> | Subject | Re: [PATCH v2 RFC] f2fs: fix to force keeping write barrier for strict fsync mode |
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On 07/14, Chao Yu wrote: > 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?
Chao, could you please post v1 with an updated description?
> > 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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