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    SubjectRE: [f2fs-dev] [PATCH 1/2] f2fs: avoid multiple node page writes due to inline_data
    Date
    Hi Jaegeuk,

    > -----Original Message-----
    > From: Jaegeuk Kim [mailto:jaegeuk@kernel.org]
    > Sent: Tuesday, January 26, 2016 3:18 AM
    > To: Chao Yu
    > Cc: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org;
    > linux-f2fs-devel@lists.sourceforge.net
    > Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: avoid multiple node page writes due to inline_data
    >
    > Hi Chao,
    >
    > On Mon, Jan 25, 2016 at 05:42:40PM +0800, Chao Yu wrote:
    > > Hi Jaegeuk,
    > >
    > > > -----Original Message-----
    > > > From: Jaegeuk Kim [mailto:jaegeuk@kernel.org]
    > > > Sent: Sunday, January 24, 2016 4:16 AM
    > > > To: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org;
    > > > linux-f2fs-devel@lists.sourceforge.net
    > > > Cc: Jaegeuk Kim
    > > > Subject: [f2fs-dev] [PATCH 1/2] f2fs: avoid multiple node page writes due to inline_data
    > > >
    > > > The sceanrio is:
    > > > 1. create fully node blocks
    > > > 2. flush node blocks
    > > > 3. write inline_data for all the node blocks again
    > > > 4. flush node blocks redundantly
    > > >
    > > > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
    > > > ---
    > > > fs/f2fs/data.c | 14 +++++++++++---
    > > > 1 file changed, 11 insertions(+), 3 deletions(-)
    > > >
    > > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
    > > > index 8d0d9ec..011456e 100644
    > > > --- a/fs/f2fs/data.c
    > > > +++ b/fs/f2fs/data.c
    > > > @@ -1622,14 +1622,22 @@ static int f2fs_write_end(struct file *file,
    > > >
    > > > trace_f2fs_write_end(inode, pos, len, copied);
    > > >
    > > > - set_page_dirty(page);
    > > > -
    > > > if (pos + copied > i_size_read(inode)) {
    > > > i_size_write(inode, pos + copied);
    > > > mark_inode_dirty(inode);
    > > > - update_inode_page(inode);
    > > > }
    > > >
    > > > + if (f2fs_has_inline_data(inode) &&
    > > > + is_inode_flag_set(F2FS_I(inode), FI_DATA_EXIST)) {
    > > > + int err = f2fs_write_inline_data(inode, page);
    > >
    > > Oh, I'm sure this can fix that issue, but IMO:
    > > a) this implementation has side-effect, it triggers inline data copying
    > > between data page and node page whenever user write inline datas, so if
    > > user updates inline data frequently, write-through approach would cause
    > > memory copy overhead.
    >
    > Agreed.
    >
    > > b) inline storm should be a rare case, as we didn't get any report about
    > > problem for long time until Dave's, and write_end is a hot path, I think
    > > it's better to be cautious to change our inline data cache policy for
    > > fixing a rare issue in hot path.
    > >
    > > What about delaying the merge operation? like:
    > > 1) as I proposed before, merging inline page into inode page when
    > > detecting free_sections <= (node_secs + 2 * dent_secs + inline_secs).
    > > 2) merge inline page into inode page before writeback inode page in
    > > sync_node_pages.
    >
    > Okay, I'm thinking more general way where we can get rid of every inlien_data
    > write when we flush node pages.

    I encountered deadlock issue, could you have a look at it?

    ======================================================
    [ INFO: possible circular locking dependency detected ]
    4.5.0-rc1 #45 Tainted: G O
    -------------------------------------------------------
    fstrim/15301 is trying to acquire lock:
    (sb_internal#2){++++..}, at: [<ffffffff81216fca>] __sb_start_write+0xda/0xf0

    but task is already holding lock:
    (&sbi->cp_rwsem){++++..}, at: [<ffffffffa07d06d2>] block_operations+0x82/0x130 [f2fs]

    which lock already depends on the new lock.


    the existing dependency chain (in reverse order) is:

    -> #1 (&sbi->cp_rwsem){++++..}:
    [<ffffffff810bf827>] lock_acquire+0xb7/0x130
    [<ffffffff817de829>] down_read+0x39/0x50
    [<ffffffffa07c27af>] f2fs_evict_inode+0x26f/0x370 [f2fs]
    [<ffffffff812326cd>] evict+0xdd/0x1d0
    [<ffffffff8123323f>] iput+0x19f/0x250
    [<ffffffff81224d9d>] do_unlinkat+0x20d/0x310
    [<ffffffff81224ee2>] SyS_unlinkat+0x22/0x40
    [<ffffffff817e0957>] entry_SYSCALL_64_fastpath+0x12/0x6f

    -> #0 (sb_internal#2){++++..}:
    [<ffffffff810bf32b>] __lock_acquire+0x132b/0x1770
    [<ffffffff810bf827>] lock_acquire+0xb7/0x130
    [<ffffffff810b8fac>] percpu_down_read+0x3c/0x80
    [<ffffffff81216fca>] __sb_start_write+0xda/0xf0
    [<ffffffffa07c2761>] f2fs_evict_inode+0x221/0x370 [f2fs]
    [<ffffffff812326cd>] evict+0xdd/0x1d0
    [<ffffffff8123323f>] iput+0x19f/0x250
    [<ffffffffa07dd4d3>] sync_node_pages+0x703/0x900 [f2fs]
    [<ffffffffa07d075a>] block_operations+0x10a/0x130 [f2fs]
    [<ffffffffa07d13e4>] write_checkpoint+0xc4/0xb80 [f2fs]
    [<ffffffffa07e0af2>] f2fs_trim_fs+0x122/0x1d0 [f2fs]
    [<ffffffffa07c07da>] f2fs_ioctl+0x7fa/0x9d0 [f2fs]
    [<ffffffff81228448>] vfs_ioctl+0x18/0x40
    [<ffffffff81228b96>] do_vfs_ioctl+0x96/0x680
    [<ffffffff81229212>] SyS_ioctl+0x92/0xa0
    [<ffffffff817e0957>] entry_SYSCALL_64_fastpath+0x12/0x6f

    other info that might help us debug this:

    Possible unsafe locking scenario:

    CPU0 CPU1
    ---- ----
    lock(&sbi->cp_rwsem);
    lock(sb_internal#2);
    lock(&sbi->cp_rwsem);
    lock(sb_internal#2);

    *** DEADLOCK ***

    Thanks,

    >
    > I've been testing this patch.
    >
    > From ebddf607c64da691fef08cf68a8ecadafd5d896b Mon Sep 17 00:00:00 2001
    > From: Jaegeuk Kim <jaegeuk@kernel.org>
    > Date: Mon, 25 Jan 2016 05:57:05 -0800
    > Subject: [PATCH] f2fs: avoid multiple node page writes due to inline_data
    >
    > The sceanrio is:
    > 1. create fully node blocks
    > 2. flush node blocks
    > 3. write inline_data for all the node blocks again
    > 4. flush node blocks redundantly
    >
    > So, this patch tries to flush inline_data when flushing node blocks.
    >
    > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
    > ---
    > fs/f2fs/data.c | 1 +
    > fs/f2fs/inline.c | 2 ++
    > fs/f2fs/node.c | 35 +++++++++++++++++++++++++++++++++++
    > fs/f2fs/node.h | 15 +++++++++++++++
    > 4 files changed, 53 insertions(+)
    >
    > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
    > index 6925c10..9043ecf 100644
    > --- a/fs/f2fs/data.c
    > +++ b/fs/f2fs/data.c
    > @@ -1464,6 +1464,7 @@ restart:
    > if (pos + len <= MAX_INLINE_DATA) {
    > read_inline_data(page, ipage);
    > set_inode_flag(F2FS_I(inode), FI_DATA_EXIST);
    > + set_inline_node(ipage);
    > sync_inode_page(&dn);
    > } else {
    > err = f2fs_convert_inline_page(&dn, page);
    > diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
    > index 8df13e5..fc4d298 100644
    > --- a/fs/f2fs/inline.c
    > +++ b/fs/f2fs/inline.c
    > @@ -159,6 +159,7 @@ no_update:
    >
    > /* clear inline data and flag after data writeback */
    > truncate_inline_inode(dn->inode_page, 0);
    > + clear_inline_node(dn->inode_page);
    > clear_out:
    > stat_dec_inline_inode(dn->inode);
    > f2fs_clear_inline_inode(dn->inode);
    > @@ -233,6 +234,7 @@ int f2fs_write_inline_data(struct inode *inode, struct page *page)
    > set_inode_flag(F2FS_I(inode), FI_DATA_EXIST);
    >
    > sync_inode_page(&dn);
    > + clear_inline_node(dn.inode_page);
    > f2fs_put_dnode(&dn);
    > return 0;
    > }
    > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
    > index 23b800d..1c5023e 100644
    > --- a/fs/f2fs/node.c
    > +++ b/fs/f2fs/node.c
    > @@ -1154,6 +1154,33 @@ void sync_inode_page(struct dnode_of_data *dn)
    > dn->node_changed = ret ? true: false;
    > }
    >
    > +static void flush_inline_data(struct f2fs_sb_info *sbi, nid_t ino)
    > +{
    > + struct inode *inode;
    > + struct page *page;
    > +
    > + inode = ilookup(sbi->sb, ino);
    > + if (!inode)
    > + return;
    > +
    > + page = find_lock_page(inode->i_mapping, 0);
    > + if (!page)
    > + goto iput_out;
    > +
    > + if (!PageDirty(page))
    > + goto put_page_out;
    > +
    > + if (!clear_page_dirty_for_io(page))
    > + goto put_page_out;
    > +
    > + if (!f2fs_write_inline_data(inode, page))
    > + inode_dec_dirty_pages(inode);
    > +put_page_out:
    > + f2fs_put_page(page, 1);
    > +iput_out:
    > + iput(inode);
    > +}
    > +
    > int sync_node_pages(struct f2fs_sb_info *sbi, nid_t ino,
    > struct writeback_control *wbc)
    > {
    > @@ -1221,6 +1248,14 @@ continue_unlock:
    > goto continue_unlock;
    > }
    >
    > + /* flush inline_data */
    > + if (!ino && is_inline_node(page)) {
    > + clear_inline_node(page);
    > + unlock_page(page);
    > + flush_inline_data(sbi, ino_of_node(page));
    > + continue;
    > + }
    > +
    > if (!clear_page_dirty_for_io(page))
    > goto continue_unlock;
    >
    > diff --git a/fs/f2fs/node.h b/fs/f2fs/node.h
    > index 23bd992..1f4f9d4 100644
    > --- a/fs/f2fs/node.h
    > +++ b/fs/f2fs/node.h
    > @@ -379,6 +379,21 @@ static inline int is_node(struct page *page, int type)
    > #define is_fsync_dnode(page) is_node(page, FSYNC_BIT_SHIFT)
    > #define is_dent_dnode(page) is_node(page, DENT_BIT_SHIFT)
    >
    > +static inline int is_inline_node(struct page *page)
    > +{
    > + return PageChecked(page);
    > +}
    > +
    > +static inline void set_inline_node(struct page *page)
    > +{
    > + SetPageChecked(page);
    > +}
    > +
    > +static inline void clear_inline_node(struct page *page)
    > +{
    > + ClearPageChecked(page);
    > +}
    > +
    > static inline void set_cold_node(struct inode *inode, struct page *page)
    > {
    > struct f2fs_node *rn = F2FS_NODE(page);
    > --
    > 2.6.3
    >


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