Messages in this thread | | | Date | Fri, 17 Dec 2021 22:44:50 +0800 | Subject | Re: [f2fs-dev] [PATCH Vx 1/1] f2fs: Avoid deadlock between writeback and checkpoint | From | Chao Yu <> |
| |
On 2021/11/20 9:50, Chao Yu wrote: > On 2021/11/18 14:46, Chao Yu wrote: >> On 2021/11/18 0:56, Jaegeuk Kim wrote: >>> On 11/09, niuzhiguo84@gmail.com wrote: >>>> From: Zhiguo Niu <zhiguo.niu@unisoc.com> >>>> >>>> There could be a scenario as following: >>>> The inodeA and inodeB are in b_io queue of writeback >>>> inodeA : f2fs's node inode >>>> inodeB : a dir inode with only one dirty pages, and the node page >>>> of inodeB cached into inodeA >>>> >>>> writeback: >>>> >>>> wb_workfn >>>> wb_writeback >>>> blk_start_plug >>>> loop { >>>> queue_io >>>> progress=__writeback_inodes_wb >>>> __writeback_single_inode >>>> do_writepages >>>> f2fs_write_data_pages >>>> wbc->pages_skipped +=get_dirty_pages >>>> inode->i_state &= ~dirty >>>> wrote++ >>>> requeue_inode >>>> } >>>> blk_finish_plug >>>> >>>> checkpoint: >>>> >>>> f2fs_write_checkpoint >>>> f2fs_sync_dirty_inodes >>>> filemap_fdatawrite >>>> do_writepages >>>> f2fs_write_data_pages >>>> f2fs_write_single_data_page >>>> f2fs_do_write_data_page >>>> set_page_writeback >>>> f2fs_outplace_write_data >>>> f2fs_update_data_blkaddr >>>> f2fs_wait_on_page_writeback >>>> inode_dec_dirty_pages >>>> >>>> 1. Writeback thread flush inodeA, and push it's bio request in task's plug; >>>> 2. Checkpoint thread writes inodeB's dirty page, and then wait its node >>>> page writeback cached into inodeA which is in writeback task's plug >>>> 3. Writeback thread flush inodeB and skip writing the dirty page as >>>> wb_sync_req[DATA] > 0. >>>> 4. As none of the inodeB's page is marked as PAGECACHE_TAG_DIRTY, writeback >>>> thread clear inodeB's dirty state. >>>> 5. Then inodeB is moved from b_io to b_dirty because of pages_skipped > 0 >>>> as checkpoint thread is stuck before dec dirty_pages. >>>> >>>> This patch collect correct pages_skipped according to the tag state in >>>> page tree of inode >>>> >>>> Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com> >>>> Signed-off-by: Jing Xia <jing.xia@unisoc.com> >>>> --- >>>> fs/f2fs/data.c | 4 +++- >>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c >>>> index f4fd6c246c9a..e98628e3868c 100644 >>>> --- a/fs/f2fs/data.c >>>> +++ b/fs/f2fs/data.c >>>> @@ -3237,7 +3237,9 @@ static int __f2fs_write_data_pages(struct address_space *mapping, >>>> return ret; >>>> >>>> skip_write: >>>> - wbc->pages_skipped += get_dirty_pages(inode); >>>> + wbc->pages_skipped += >>>> + mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY) ? >>> >>> Is there any race condition to get 0, if there's any dirty page? IOWs, it >> >> Quoted from Jing Xia's explanation: >> >> [T:writeback] [T:checkpoint] > > My bad, [1] should be here: > > bio contains NodeA was plugged in writeback threads > > Thanks, > >> - do_writepages -- sync write inodeB, inc wb_sync_req[DATA] >> - f2fs_write_data_pages >> - f2fs_write_single_data_page -- write last dirty page >> - f2fs_do_write_data_page >> - set_page_writeback -- clear page dirty flag and >> PAGECACHE_TAG_DIRTY tag in radix tree >> - f2fs_outplace_write_data >> - f2fs_update_data_blkaddr >> - f2fs_wait_on_page_writeback -- wait NodeA to writeback here
Jaegeuk,
checkpoint() will stuck on waiting NodeA to writeback.
>> - inode_dec_dirty_pages > >> bio contains NodeA was plugged in writeback threads > > [1] > > Thanks, > >> - writeback_sb_inodes >> - writeback_single_inode >> - do_writepages >> - f2fs_write_data_pages -- skip writepages due to wb_sync_req[DATA] >> - wbc->pages_skipped += get_dirty_pages() -- PAGECACHE_TAG_DIRTY is not set but get_dirty_pages() returns one >> - requeue_inode -- requeue inode to wb->b_dirty queue due to non-zero.pages_skipped
Meanwhile, kworker plugged NodeA, and then loop writebacking inode due to inode will be requeued all the time.
Thanks,
>> >>> seems the current condition is just requeuing the inode as dirty, but next >>> flushing time will remove it from dirty list. Is this giving too much overheads? >> >> I prefer to let writeback thread call blk_flush_plug() after skipping >> writepages() due to wb_sync_req[DATA/NODE] check condition, thoughts? >> >> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c >> index 9f754aaef558..b6e1ed73f8f5 100644 >> --- a/fs/f2fs/data.c >> +++ b/fs/f2fs/data.c >> @@ -3087,6 +3087,8 @@ static int f2fs_write_cache_pages(struct address_space *mapping, >> /* give a priority to WB_SYNC threads */ >> if (atomic_read(&sbi->wb_sync_req[DATA]) && >> wbc->sync_mode == WB_SYNC_NONE) { >> + if (current->plug) >> + blk_flush_plug(current->plug, false); >> done = 1; >> break; >> } >> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c >> index 556fcd8457f3..dd9a817d8dab 100644 >> --- a/fs/f2fs/node.c >> +++ b/fs/f2fs/node.c >> @@ -1946,6 +1946,8 @@ int f2fs_sync_node_pages(struct f2fs_sb_info *sbi, >> if (atomic_read(&sbi->wb_sync_req[NODE]) && >> wbc->sync_mode == WB_SYNC_NONE) { >> done = 1; >> + if (current->plug) >> + blk_flush_plug(current->plug, false); >> break; >> } >> >> >> >> Thanks, >> >>> >>>> + get_dirty_pages(inode) : 0; >>>> trace_f2fs_writepages(mapping->host, wbc, DATA); >>>> return 0; >>>> } >>>> -- >>>> 2.28.0 >> >> >> _______________________________________________ >> 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
| |