Messages in this thread | | | Date | Sat, 20 Nov 2021 09:50:20 +0800 | Subject | Re: [f2fs-dev] [PATCH Vx 1/1] f2fs: Avoid deadlock between writeback and checkpoint | From | Chao Yu <> |
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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 > - 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 > >> 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 >
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