From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932158AbcAHMGo (ORCPT ); Fri, 8 Jan 2016 07:06:44 -0500 Received: from mailout3.samsung.com ([203.254.224.33]:38400 "EHLO mailout3.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750794AbcAHMGl (ORCPT ); Fri, 8 Jan 2016 07:06:41 -0500 X-AuditID: cbfee61b-f793c6d00000236c-93-568fa64f715b From: Chao Yu To: "'Jaegeuk Kim'" Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net References: <00a901d141e6$e42ec950$ac8c5bf0$@samsung.com> <20151230000513.GA13809@jaegeuk.local> <00dc01d142a2$5920ec00$0b62c400$@samsung.com> <20151230194102.GD28564@jaegeuk.local> <011701d143ac$183be770$48b3b650$@samsung.com> <20160101035024.GB6673@jaegeuk.local> <56866D6F.7040509@kernel.org> In-reply-to: <56866D6F.7040509@kernel.org> Subject: RE: [f2fs-dev] [PATCH 2/2] f2fs: support revoking atomic written pages Date: Fri, 08 Jan 2016 20:05:52 +0800 Message-id: <005701d14a0d$030ed8f0$092c8ad0$@samsung.com> MIME-version: 1.0 Content-type: text/plain; charset=us-ascii Content-transfer-encoding: 7bit X-Mailer: Microsoft Outlook 14.0 Thread-index: AQFsZF8AOfvUSv/TFfZXLnmyjFz4aQHU9ZHDAggwKoECGzOmpwIpFhwvAUUV3k0BhZ3ae59j4eFA Content-language: zh-cn X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFnrMLMWRmVeSWpSXmKPExsVy+t9jQV3/Zf1hBl9e6Fk8WT+L2eLSIneL y7vmsDkwe2xa1cnmsXvBZyaPz5vkApijuGxSUnMyy1KL9O0SuDLunlzGVnA5s+L2/Y/sDYyv g7sYOTkkBEwk5l0+xQZhi0lcuLceyObiEBKYxSgx68BLdgjnFaPEx1VrmUCq2ARUJJZ3/Aez RQTUJHr3TQGyOTiYBTwkdh0rhajfyCQxa+J3RpAaTgEtidb515lBbGEBf4lT89vAbBYBVYmV Bw6AzeEVsJTYuPkplC0o8WPyPRYQmxmod/3O40wQtrzE5jVvmSEuVZDYcfY1I8heEYEYicZ/ 9RAl4hIbj9ximcAoNAvJpFlIJs1CMmkWkpYFjCyrGCVSC5ILipPSc43yUsv1ihNzi0vz0vWS 83M3MYKD/pn0DsbDu9wPMQpwMCrx8HLs6AsTYk0sK67MPcQowcGsJMK7qLg/TIg3JbGyKrUo P76oNCe1+BCjNAeLkjjvvkuRYUIC6YklqdmpqQWpRTBZJg5OqQbGbEmDleGhyeZbRNuPfd0m sNla8eovj52rbqd+vf/xrUzEoc8/3Ezz/N+HK+9b/6A+/VuzX0LqY4Ytbulayd9SzScXe+zZ uu+dmppQeQarZMTXLcuMXjrZT75kdU/c+OM8iTxrrjbx7fu1nfV6YxNrgl7MLz/zbK2C6b7P t3VXp571qHj1cqOfEktxRqKhFnNRcSIAkecP+HYCAAA= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jaegeuk, Any progress on this patch? Thanks, > -----Original Message----- > From: Chao Yu [mailto:chao@kernel.org] > Sent: Friday, January 01, 2016 8:14 PM > To: Jaegeuk Kim > Cc: linux-kernel@vger.kernel.org; linux-f2fs-devel@lists.sourceforge.net > Subject: Re: [f2fs-dev] [PATCH 2/2] f2fs: support revoking atomic written pages > > Hi Jaegeuk, > > On 1/1/16 11:50 AM, Jaegeuk Kim wrote: > > Hi Chao, > > > > ... > > > >>>>> On Tue, Dec 29, 2015 at 11:12:36AM +0800, Chao Yu wrote: > >>>>>> f2fs support atomic write with following semantics: > >>>>>> 1. open db file > >>>>>> 2. ioctl start atomic write > >>>>>> 3. (write db file) * n > >>>>>> 4. ioctl commit atomic write > >>>>>> 5. close db file > >>>>>> > >>>>>> With this flow we can avoid file becoming corrupted when abnormal power > >>>>>> cut, because we hold data of transaction in referenced pages linked in > >>>>>> inmem_pages list of inode, but without setting them dirty, so these data > >>>>>> won't be persisted unless we commit them in step 4. > >>>>>> > >>>>>> But we should still hold journal db file in memory by using volatile write, > >>>>>> because our semantics of 'atomic write support' is not full, in step 4, we > >>>>>> could be fail to submit all dirty data of transaction, once partial dirty > >>>>>> data was committed in storage, db file should be corrupted, in this case, > >>>>>> we should use journal db to recover the original data in db file. > >>>>> > >>>>> Originally, IOC_ABORT_VOLATILE_WRITE was supposed to handle commit failures, > >>>>> since database should get its error literally. > >>>>> > >>>>> So, the only thing that we need to do is keeping journal data for further db > >>>>> recovery. > >>>> > >>>> IMO, if we really support *atomic* interface, we don't need any journal data > >>>> kept by user, because f2fs already have it in its storage since we always > >>>> trigger OPU for pages written in atomic-write opened file, f2fs can easily try > >>>> to revoke (replace old to new in metadata) when any failure exist in atomic > >>>> write process. > >>> > >>> Yeah, so current design does not fully support atomic writes. IOWs, volatile > >>> writes for journal files should be used together to minimize sqlite change as > >>> much as possible. > >>> > >>>> But in current design, we still hold journal data in memory for recovering for > >>>> *rare* failure case. I think there are several issues: > >>>> a) most of time, we are in concurrent scenario, so if large number of journal > >>>> db files were opened simultaneously, we are under big memory pressure. > >>> > >>> In current android, I've seen that this is not a big concern. Even there is > >>> memory pressure, f2fs flushes volatile pages. > >> > >> When I change to redirty all volatile pages in ->writepage, android seems go > >> into an infinite loop when doing recovery flow of f2fs data partition in startup. > >> > >> if (f2fs_is_volatile_file(inode)) > >> goto redirty_out; > > > > Where did you put this? It doesn't flush at all? Why? > > Original place in ->writepage, just remove two other conditions. > > To avoid potential random writebacking of dirty page in journal which > cause unpredicted corrupting in journal. > > > Practically, the peak amount of journal writes depend on how many transactions > > are processing concurrently. > > I mean, in-memory pages are dropped at the end of every transaction. > > You can check the number of pages through f2fs_stat on your phone. > > > >> I didn't dig details, but I think there may be a little risk for this design. > >> > >>> > >>>> b) If we are out of memory, reclaimer tries to write page of journal db into > >>>> disk, it will destroy db file. > >>> > >>> I don't understand. Could you elaborate why journal writes can corrupt db? > >> > >> Normally, we keep pages of journal in memory, but partial page in journal > >> will be write out to device by reclaimer when out of memory. So this journal > >> may have valid data in its log head, but with corrupted data, then after > >> abnormal powe-cut, recovery with this journal before a transaction will > >> destroy db. Right? > > > > Just think about sqlite without this feature. > > Broken journal is pretty normal case for sqlite. > > Maybe, if it is caused by bug or design issue of software, no matter db system > or filesystem, we should try our best to fix it to avoid generating broken journals. > > > > >>> > >>>> c) Though, we have journal db file, we will face failure of recovering db file > >>>> from journal db due to ENOMEM or EIO, then db file will be corrupted. > >>> > >>> Do you mean the failure of recovering db with a complete journal? > >>> Why do we have to handle that? That's a database stuff, IMO. > >> > >> Yes, just list for indicating we will face the same issue which is hard to > >> handle both in original design and new design, so the inner revoking failure > >> issue would not be a weak point or flaw of new design. > >> > >>> > >>>> d) Recovery flow will make data page dirty, triggering both data stream and > >>>> metadata stream, there should be more IOs than in inner revoking in > >>>> atomic-interface. > >>> > >>> Well, do you mean there is no need to recover db after revoking? > >> > >> Yes, revoking make the same effect like the recovery of sqlite, so after > >> revoking, recovery is no need. > > > > Logically, it doesn't make sense. If there is a valid journal file, it should > > redo the previous transaction. No? > > As we know, in sqlite, before we commit a transaction, we will use journal to > record original data of pages which will be updated in following transaction, so > in following if a) abnormal power-cut, b) commit error, c) redo command was > triggered by user, we will recover db with journal. > > Ideally, if we support atomic write interface, in there should always return two > status in atomic write interface: success or fail. If success, transaction was > committed, otherwise, it looks like nothing happened, user will be told > transaction was failed. Then, journals in sqlite could no longer be used, > eventually no journal, no recovery. > > The only thing we should concern is inner failure (e.g. ENOMEM, ENOSPC) of > revoking in commit interface since it could destroy db file permanently w/o > journal. IMO, some optimization could be done for these cases: > 1. ENOMEM: enable retrying or mark accessed flag in page in advance. > 2. ENOSPC: preallocate blocks for node blocks and data blocks. > > These optimizations couldn't guarantee no failure in revoking operation > completely, luckily, those are not common cases, and they also happen in sqlite > w/o atomic feature. > > One more possible proposal is: if we support reflink feature like ocfs2/xfs, I > guess we can optimize DB like: > 1. reflink db to db.ref > 2. do transaction in db.ref > - failed, rm db.ref > - power-cut rm db.ref > 3. rename db.ref to db > > > > >> One more case is that user can send a command to abort current transaction, > >> it should be happened before atomic_commit operation, which could easily > >> handle with abort_commit ioctl. > >> > >>> > >>>> e) Moreover, there should be a hole between 1) commit fail and 2) abort write & > >>>> recover, checkpoint will persist the corrupt data in db file, following abnormal > >>>> power-cut will leave that data in disk. > >>> > >>> Yes, in that case, database should recover corrupted db with its journal file. > >> > >> Journal could be corrupted as I descripted in b). > > > > Okay, so what I'm thinking is like this. > > It seems there are two corruption cases after journal writes. > > > > 1. power cut during atomic writes > > - broken journal file and clean db file -> give up > > - luckily, valid journal file and clean db file -> recover db > > > > 2. error during atomic writes > > a. power-cut before abort completion > > - broken journal file and broken db file -> revoking is needed! > > > > b. after abort > > - valid journal file and broken db file -> recover db (likewise plain sqlite) > > > > Indeed, in the 2.a. case, we need revoking; I guess that's what you mentioned. > > But, I think, even if revoking is done, we should notify an error to abort and > > recover db by 2.b. > > > > Something like this after successful revoking. > > > > 1. power cut during atomic writes > > - broken journal file and clean db file -> give up > > - luckily, valid journal file and clean db file -> recover db > > > > 2. error during atomic writes w/ revoking > > a. power-cut before abort completion > > - broken journal file and clean db file -> give up > > - luckily, valid journal file and clean db file -> recover db > > > > b. after abort > > - valid journal file and clean db file -> recover db > > That's right. > > > > > Let me verify these scenarios first. :) > > OK. :) > > Thanks, > > > > > Thanks, > > > >>> > >>>> With revoking supported design, we can not solve all above issues, we will still > >>>> face the same issue like c), but it will be a big improve if we can apply this > >>>> in our interface, since it provide a way to fix the issue a) b) d). And also for > >>>> e) case, we try to rescue data in first time that our revoking operation would be > >>>> protected by f2fs_lock_op to avoid checkpoint + power-cut. > >>>> > >>>> If you don't want to have a big change in this interface or recovery flow, how > >>>> about keep them both, and add a mount option to control inner recovery flow? > >>> > >>> Hmm, okay. I believe the current design is fine for sqlite in android. > >> > >> I believe new design will enhance in memory usage and error handling of sqlite > >> in android, and hope this can be applied. But, I can understand that if you > >> were considerring about risk control and backward compatibility, since this > >> change affects all atomic related ioctls. > >> > >>> For other databases, I can understand that they can use atomic_write without > >>> journal control, which is a sort of stand-alone atomic_write. > >>> > >>> It'd better to add a new ioctl for that, but before adding it, can we find > >>> any usecase for this feature? (e.g., postgresql, mysql, mariadb, couchdb?) > >> > >> You mean investigating or we can only start when there is a clear commercial > >> demand ? > >> > >>> Then, I expect that we can define a more appropriate and powerful ioctl. > >> > >> Agreed :) > >> > >> Thanks, > >> > >>> > >>> Thanks, > >>> > >>>> > >>>> How do you think? :) > >>>> > >>>> Thanks, > >>>> > >>>>> But, unfortunately, it seems that something is missing in the > >>>>> current implementation. > >>>>> > >>>>> So simply how about this? > >>>>> > >>>>> A possible flow would be: > >>>>> 1. write journal data to volatile space > >>>>> 2. write db data to atomic space > >>>>> 3. in the error case, call ioc_abort_volatile_writes for both journal and db > >>>>> - flush/fsync journal data to disk > >>>>> - drop atomic data, and will be recovered by database with journal > >>>>> > >>>>> From cb33fc8bc30981c370ec70fe68871130109793ec Mon Sep 17 00:00:00 2001 > >>>>> From: Jaegeuk Kim > >>>>> Date: Tue, 29 Dec 2015 15:46:33 -0800 > >>>>> Subject: [PATCH] f2fs: fix f2fs_ioc_abort_volatile_write > >>>>> > >>>>> There are two rules to handle aborting volatile or atomic writes. > >>>>> > >>>>> 1. drop atomic writes > >>>>> - we don't need to keep any stale db data. > >>>>> > >>>>> 2. write journal data > >>>>> - we should keep the journal data with fsync for db recovery. > >>>>> > >>>>> Signed-off-by: Jaegeuk Kim > >>>>> --- > >>>>> fs/f2fs/file.c | 13 ++++++++++--- > >>>>> 1 file changed, 10 insertions(+), 3 deletions(-) > >>>>> > >>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c > >>>>> index 91f576a..d16438a 100644 > >>>>> --- a/fs/f2fs/file.c > >>>>> +++ b/fs/f2fs/file.c > >>>>> @@ -1433,9 +1433,16 @@ static int f2fs_ioc_abort_volatile_write(struct file *filp) > >>>>> if (ret) > >>>>> return ret; > >>>>> > >>>>> - clear_inode_flag(F2FS_I(inode), FI_ATOMIC_FILE); > >>>>> - clear_inode_flag(F2FS_I(inode), FI_VOLATILE_FILE); > >>>>> - commit_inmem_pages(inode, true); > >>>>> + if (f2fs_is_atomic_file(inode)) { > >>>>> + clear_inode_flag(F2FS_I(inode), FI_ATOMIC_FILE); > >>>>> + commit_inmem_pages(inode, true); > >>>>> + } > >>>>> + if (f2fs_is_volatile_file(inode)) { > >>>>> + clear_inode_flag(F2FS_I(inode), FI_VOLATILE_FILE); > >>>>> + ret = commit_inmem_pages(inode, false); > >>>>> + if (!ret) > >>>>> + ret = f2fs_sync_file(filp, 0, LLONG_MAX, 0); > >>>>> + } > >>>>> > >>>>> mnt_drop_write_file(filp); > >>>>> return ret; > >>>>> -- > >>>>> 2.6.3 > >>>> > > > > ------------------------------------------------------------------------------ > > _______________________________________________ > > Linux-f2fs-devel mailing list > > Linux-f2fs-devel@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel > > > > ------------------------------------------------------------------------------ > _______________________________________________ > Linux-f2fs-devel mailing list > Linux-f2fs-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel