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Date: Thu, 24 Dec 2015 13:51:53 -0800
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao2.yu@...sung.com>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 3/4] f2fs: avoid f2fs_lock_op in
f2fs_write_begin
Hi Chao,
On Thu, Dec 24, 2015 at 12:33:50PM -0800, Jaegeuk Kim wrote:
> Hi Chao,
>
> On Thu, Dec 24, 2015 at 01:50:32PM +0800, Chao Yu wrote:
> > Hi Jaegeuk,
> >
> > > -----Original Message-----
> > > From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> > > Sent: Thursday, December 24, 2015 10:15 AM
> > > To: linux-kernel@...r.kernel.org; linux-fsdevel@...r.kernel.org;
> > > linux-f2fs-devel@...ts.sourceforge.net
> > > Cc: Jaegeuk Kim
> > > Subject: [f2fs-dev] [PATCH 3/4] f2fs: avoid f2fs_lock_op in f2fs_write_begin
> > >
> > > If f2fs_write_begin is to update data, we can bypass calling f2fs_lock_op() in
> > > order to avoid the checkpoint latency in the write syscall.
> > >
> > > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > > ---
> > > fs/f2fs/data.c | 43 ++++++++++++++++++++++++++++++++++---------
> > > 1 file changed, 34 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > > index 49092da..d53cf4f 100644
> > > --- a/fs/f2fs/data.c
> > > +++ b/fs/f2fs/data.c
> > > @@ -1418,10 +1418,16 @@ static int prepare_write_begin(struct f2fs_sb_info *sbi,
> > > pgoff_t index = page->index;
> > > struct dnode_of_data dn;
> > > struct page *ipage;
> > > + bool locked = false;
> > > + struct extent_info ei;
> > > int err = 0;
> > >
> > > - f2fs_lock_op(sbi);
> > > -
> > > + if (f2fs_has_inline_data(inode) ||
> > > + (pos & PAGE_CACHE_MASK) >= i_size_read(inode)) {
> > > + f2fs_lock_op(sbi);
> > > + locked = true;
> > > + }
> > > +restart:
> > > /* check inline_data */
> > > ipage = get_node_page(sbi, inode->i_ino);
> > > if (IS_ERR(ipage)) {
> > > @@ -1436,22 +1442,41 @@ static int prepare_write_begin(struct f2fs_sb_info *sbi,
> > > read_inline_data(page, ipage);
> > > set_inode_flag(F2FS_I(inode), FI_DATA_EXIST);
> > > sync_inode_page(&dn);
> > > - goto done;
> > > } else {
> > > err = f2fs_convert_inline_page(&dn, page);
> > > if (err)
> > > - goto err_out;
> > > + goto out;
> > > + err = f2fs_get_block(&dn, index);
> >
> > Seems after f2fs_convert_inline_page, data_blkaddr and node_changed should
> > have been set, so f2fs_get_block could be removed here.
>
> I don't think so. The inline_data treats with 0'th index only.
> In order to handle non-zero index, we should do f2fs_get_block.
> Oh, if you meant zero index case only, we can do that like this.
>
> if (index)
> err = f2fs_get_block();
Actually, we need
if (index || !dn.data_blkaddr)
err = f2fs_get_block();
Since f2fs_convert_inline_page can return right away, if there is
no data in inline_data space.
Thanks,
>
> >
> > > + }
> > > + } else if (locked) {
> > > + err = f2fs_get_block(&dn, index);
> > > + } else {
> > > + if (f2fs_lookup_extent_cache(inode, index, &ei)) {
> > > + dn.data_blkaddr = ei.blk + index - ei.fofs;
> > > + } else {
> > > + bool restart = false;
> > > +
> > > + /* hole case */
> > > + err = get_dnode_of_data(&dn, index, LOOKUP_NODE);
> >
> > Better to handle error case like -ENOMEM or -EIO.
>
> I think we can just give another chance at this moment and let f2fs_get_block()
> handle that in the next round.
>
> Thanks,
>
> >
> > Thanks,
> >
> > > + if (err || (!err && dn.data_blkaddr == NULL_ADDR))
> > > + restart = true;
> > > + if (restart) {
> > > + f2fs_put_dnode(&dn);
> > > + f2fs_lock_op(sbi);
> > > + locked = true;
> > > + goto restart;
> > > + }
> > > }
> > > }
> > > - err = f2fs_get_block(&dn, index);
> > > -done:
> > > +
> > > /* convert_inline_page can make node_changed */
> > > *blk_addr = dn.data_blkaddr;
> > > *node_changed = dn.node_changed;
> > > -err_out:
> > > +out:
> > > f2fs_put_dnode(&dn);
> > > unlock_out:
> > > - f2fs_unlock_op(sbi);
> > > + if (locked)
> > > + f2fs_unlock_op(sbi);
> > > return err;
> > > }
> > >
> > > @@ -1488,7 +1513,7 @@ repeat:
> > >
> > > *pagep = page;
> > >
> > > - err = prepare_write_begin(sbi, page, pos + len,
> > > + err = prepare_write_begin(sbi, page, pos, len,
> > > &blkaddr, &need_balance);
> > > if (err)
> > > goto fail;
> > > --
> > > 2.5.4 (Apple Git-61)
> > >
> > >
> > > ------------------------------------------------------------------------------
> > > _______________________________________________
> > > Linux-f2fs-devel mailing list
> > > Linux-f2fs-devel@...ts.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>
> ------------------------------------------------------------------------------
> _______________________________________________
> Linux-f2fs-devel mailing list
> Linux-f2fs-devel@...ts.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
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