Re: [PATCH] f2fs: provide f2fs_balance_fs to __write_data_page for dentry pages

From: Jaegeuk Kim
Date: Thu Aug 03 2017 - 21:57:50 EST

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On 08/02, Yunlong Song wrote:
> Hi Jay,
> The case is like this:
> write_checkpoint: normal dentry
> page writeback of inodeBï
> -block_operations -f2fs_write_data_pages
> -SBI_BLOCK_OPS is set -f2fs_write_cache_pages
> -sync_dirty_inodes -__write_data_page
> -retry: -test SBI_BLOCK_OPS is set and skip
> f2fs_balance_fs
> inodeA <- list_first_entry(dirty_list)
> filemap_fdatawrite(inodeA)
> goto retry
> -SBI_BLOCK_OPS is clear
>
> write_checkpoint flow call sync_dirty_inodes to traversal the dirty inode
> list and filemap_fdatawrite each inode,
> during this period, if normal dentry_page writeback is processing inodeB,
> and syc_dirty_inodes is processing
> inodeA, then inodeB writeback flow will skip f2fs_balance_fs and may write
> the dentry page to reserved segments.

If there are not enough sections, all the possible system calls were already
blocked by gc_mutex. So, it doesn't have to do f2fs_balance_fs(), and let
sync_dirty_inodes() flush dentry pages of inodeB.

Oh, does it make livelock?

- f2fs_balance_fs
- f2fs_gc
- write_checkpoint
- sync_dirty_inodes
- filemap_fdatawrite(inodeB)
- __write_data_page
- f2fs_balance_fs again?

>
> On 2017/8/2 2:22, Jaegeuk Kim wrote:
> > On 08/01, Yunlong Song wrote:
> > > Hi Jay,
> > > The SBI_BLOCK_OPS can not cover all the case, once SBI_BLOCK_OPS is set,
> > > all the normal writeback
> > > (before the SBI_BLOCK_OPS is clear) of dentry pages which do not come from
> > > write_checkpoint flow will
> > > totally miss all the f2fs_balance_fs check.
> > Why not? There must be no dirty dentry pages after sync_dirty_inodes() in that
> > period which we grabbed the globla lock.
> >
> > Thanks,
> >
> > > On 2017/7/31 0:05, Yunlong Song wrote:
> > > > Hi Jay,
> > > > Chao has pointed out one reason, besides, I have another reason: we
> > > > should take care of writeback for f2fs_balance_fs carefully, because if
> > > > some bugs cause reserved segments unlikely used, which means
> > > > f2fs_balance_fs does not work or is skipped in some corner case that we
> > > > have not noticed or found out yet, then the reserved segments may be
> > > > continually used and even used up in the writeback process of dentry
> > > > page, since current design believe in the f2fs_balance_fs in system
> > > > call and has no check in denty page writeback. To avoid this, we can put
> > > > a f2fs_balance_fs in the dentry page writeback process to give f2fs more
> > > > robust in free segments reserved. This is worth, because free segments
> > > > reserved are so important, if they are used up, f2fs will enter a
> > > > totally wrong status and make a wrong image.
> > > >
> > > > On 07/30/2017 15:31, Jaegeuk Kim <mailto:jaegeuk@xxxxxxxxxx> wrote:
> > > >
> > > > On 07/29, Yunlong Song wrote:
> > > > > f2fs_balance_fs of dentry pages is skipped in __write_data_page
> > > > due to deadlock
> > > > > of gc_mutex in write_checkpoint flow. This patch enables
> > > > f2fs_balance_fs for
> > > > > normal dentry page writeback to ensure there are always enough
> > > > free segments.
> > > >
> > > > Sorry, by the way, why do we need to do this? I subtly thought
> > > > that dirty node
> > > > pages can be produce by redirtied inodes from what we've not
> > > > covered through
> > > > filesystem calls. But, in dentry pages, we're controlling the
> > > > number of dirty
> > > > pages, and calling f2fs_balance_fs in each directory operations.
> > > >
> > > > Chao?
> > > >
> > > > Thanks,
> > > >
> > > > >
> > > > > Reported-by: Chao Yu <yuchao0@xxxxxxxxxx>
> > > > > Signed-off-by: Yunlong Song <yunlong.song@xxxxxxxxxx>
> > > > > ---
> > > > > fs/f2fs/checkpoint.c | 2 +-
> > > > > fs/f2fs/data.c | 67
> > > > +++++++++++++++++++++++++++++++++++++++++++++-------
> > > > > fs/f2fs/f2fs.h | 1 +
> > > > > 3 files changed, 61 insertions(+), 9 deletions(-)
> > > > >
> > > > > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > > > > index 3c84a25..2882878 100644
> > > > > --- a/fs/f2fs/checkpoint.c
> > > > > +++ b/fs/f2fs/checkpoint.c
> > > > > @@ -904,7 +904,7 @@ int sync_dirty_inodes(struct f2fs_sb_info
> > > > *sbi, enum inode_type type)
> > > > > if (inode) {
> > > > > unsigned long cur_ino = inode->i_ino;
> > > > >
> > > > > - filemap_fdatawrite(inode->i_mapping);
> > > > > + f2fs_filemap_fdatawrite(inode->i_mapping, is_dir);
> > > > > iput(inode);
> > > > > /* We need to give cpu to another writers. */
> > > > > if (ino == cur_ino) {
> > > > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > > > > index aefc2a5..ed7efa5 100644
> > > > > --- a/fs/f2fs/data.c
> > > > > +++ b/fs/f2fs/data.c
> > > > > @@ -1475,7 +1475,7 @@ int do_write_data_page(struct f2fs_io_info
> > > > *fio)
> > > > > }
> > > > >
> > > > > static int __write_data_page(struct page *page, bool *submitted,
> > > > > - struct writeback_control *wbc)
> > > > > + struct writeback_control *wbc, bool do_balance)
> > > > > {
> > > > > struct inode *inode = page->mapping->host;
> > > > > struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> > > > > @@ -1578,7 +1578,7 @@ static int __write_data_page(struct page
> > > > *page, bool *submitted,
> > > > > }
> > > > >
> > > > > unlock_page(page);
> > > > > - if (!S_ISDIR(inode->i_mode))
> > > > > + if (do_balance)
> > > > > f2fs_balance_fs(sbi, need_balance_fs);
> > > > >
> > > > > if (unlikely(f2fs_cp_error(sbi))) {
> > > > > @@ -1602,7 +1602,7 @@ static int __write_data_page(struct page
> > > > *page, bool *submitted,
> > > > > static int f2fs_write_data_page(struct page *page,
> > > > > struct writeback_control *wbc)
> > > > > {
> > > > > - return __write_data_page(page, NULL, wbc);
> > > > > + return __write_data_page(page, NULL, wbc, true);
> > > > > }
> > > > >
> > > > > /*
> > > > > @@ -1611,7 +1611,7 @@ static int f2fs_write_data_page(struct
> > > > page *page,
> > > > > * warm/hot data page.
> > > > > */
> > > > > static int f2fs_write_cache_pages(struct address_space *mapping,
> > > > > - struct writeback_control *wbc)
> > > > > + struct writeback_control *wbc, bool
> > > > do_balance)
> > > > > {
> > > > > int ret = 0;
> > > > > int done = 0;
> > > > > @@ -1701,7 +1701,7 @@ static int f2fs_write_cache_pages(struct
> > > > address_space *mapping,
> > > > > if (!clear_page_dirty_for_io(page))
> > > > > goto continue_unlock;
> > > > >
> > > > > - ret = __write_data_page(page, &submitted, wbc);
> > > > > + ret = __write_data_page(page, &submitted, wbc,
> > > > do_balance);
> > > > > if (unlikely(ret)) {
> > > > > /*
> > > > > * keep nr_to_write, since vfs uses this to
> > > > > @@ -1756,8 +1756,8 @@ static int f2fs_write_cache_pages(struct
> > > > address_space *mapping,
> > > > > return ret;
> > > > > }
> > > > >
> > > > > -static int f2fs_write_data_pages(struct address_space *mapping,
> > > > > - struct writeback_control *wbc)
> > > > > +static int _f2fs_write_data_pages(struct address_space *mapping,
> > > > > + struct writeback_control *wbc, bool do_balance)
> > > > > {
> > > > > struct inode *inode = mapping->host;
> > > > > struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> > > > > @@ -1794,7 +1794,7 @@ static int f2fs_write_data_pages(struct
> > > > address_space *mapping,
> > > > > goto skip_write;
> > > > >
> > > > > blk_start_plug(&plug);
> > > > > - ret = f2fs_write_cache_pages(mapping, wbc);
> > > > > + ret = f2fs_write_cache_pages(mapping, wbc, do_balance);
> > > > > blk_finish_plug(&plug);
> > > > >
> > > > > if (wbc->sync_mode == WB_SYNC_ALL)
> > > > > @@ -1813,6 +1813,57 @@ static int f2fs_write_data_pages(struct
> > > > address_space *mapping,
> > > > > return 0;
> > > > > }
> > > > >
> > > > > +static int f2fs_write_data_pages(struct address_space *mapping,
> > > > > + struct writeback_control *wbc)
> > > > > +{
> > > > > + return _f2fs_write_data_pages(mapping, wbc, true);
> > > > > +}
> > > > > +
> > > > > +/*
> > > > > + * This function was copied from do_writepages from
> > > > mm/page-writeback.c.
> > > > > + * The major change is changing writepages to
> > > > _f2fs_write_data_pages.
> > > > > + */
> > > > > +static int f2fs_do_writepages(struct address_space *mapping,
> > > > > + struct writeback_control *wbc, bool is_dir)
> > > > > +{
> > > > > + int ret;
> > > > > +
> > > > > + if (wbc->nr_to_write <= 0)
> > > > > + return 0;
> > > > > + while (1) {
> > > > > + ret = _f2fs_write_data_pages(mapping, wbc, !is_dir);
> > > > > + if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL))
> > > > > + break;
> > > > > + cond_resched();
> > > > > + congestion_wait(BLK_RW_ASYNC, HZ/50);
> > > > > + }
> > > > > + return ret;
> > > > > +}
> > > > > +
> > > > > +/*
> > > > > + * This function was copied from __filemap_fdatawrite_range from
> > > > > + * mm/filemap.c. The major change is changing do_writepages to
> > > > > + * f2fs_do_writepages.
> > > > > + */
> > > > > +int f2fs_filemap_fdatawrite(struct address_space *mapping, bool
> > > > is_dir)
> > > > > +{
> > > > > + int ret;
> > > > > + struct writeback_control wbc = {
> > > > > + .sync_mode = WB_SYNC_ALL,
> > > > > + .nr_to_write = LONG_MAX,
> > > > > + .range_start = 0,
> > > > > + .range_end = LLONG_MAX,
> > > > > + };
> > > > > +
> > > > > + if (!mapping_cap_writeback_dirty(mapping))
> > > > > + return 0;
> > > > > +
> > > > > + wbc_attach_fdatawrite_inode(&wbc, mapping->host);
> > > > > + ret = f2fs_do_writepages(mapping, &wbc, is_dir);
> > > > > + wbc_detach_inode(&wbc);
> > > > > + return ret;
> > > > > +}
> > > > > +
> > > > > static void f2fs_write_failed(struct address_space *mapping,
> > > > loff_t to)
> > > > > {
> > > > > struct inode *inode = mapping->host;
> > > > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > > > > index 9280283..ea9bebb 100644
> > > > > --- a/fs/f2fs/f2fs.h
> > > > > +++ b/fs/f2fs/f2fs.h
> > > > > @@ -2572,6 +2572,7 @@ void f2fs_invalidate_page(struct page
> > > > *page, unsigned int offset,
> > > > > int f2fs_migrate_page(struct address_space *mapping, struct
> > > > page *newpage,
> > > > > struct page *page, enum migrate_mode mode);
> > > > > #endif
> > > > > +int f2fs_filemap_fdatawrite(struct address_space *mapping, bool
> > > > is_dir);
> > > > >
> > > > > /*
> > > > > * gc.c
> > > > > --
> > > > > 1.8.5.2
> > > >
> > > --
> > > Thanks,
> > > Yunlong Song
> > >
> > .
> >
>
> --
> Thanks,
> Yunlong Song
>

Next message: Jaegeuk Kim: "[PATCH] f2fs: use printk_ratelimited for f2fs_msg"
Previous message: Finley Xiao: "[PATCH] cpufreq: dt: Add rk3328 compatible to use generic cpufreq driver"
In reply to: Yunlong Song: "Re: [PATCH] f2fs: provide f2fs_balance_fs to __write_data_page for dentry pages"
Next in thread: Yunlong Song: "Re: [PATCH] f2fs: provide f2fs_balance_fs to __write_data_page for dentry pages"
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