Messages in this thread | | | From | Chao Yu <> | Subject | RE: [RFC PATCH] f2fs: add extent cache base on rb-tree | Date | Mon, 22 Dec 2014 17:06:52 +0800 |
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Hi Changman,
> -----Original Message----- > From: Changman Lee [mailto:cm224.lee@samsung.com] > Sent: Monday, December 22, 2014 10:03 AM > To: Chao Yu > Cc: Jaegeuk Kim; linux-f2fs-devel@lists.sourceforge.net; linux-kernel@vger.kernel.org > Subject: Re: [RFC PATCH] f2fs: add extent cache base on rb-tree > > Hi Yu, > > Good approach. > As you know, however, f2fs breaks extent itself due to COW. > Unlike other filesystem like btrfs, minimum extent of f2fs could have 4KB granularity. > So we would have lots of extents per inode and it could lead to overhead > to manage extents. > > Anyway, mount option could be alternative for this patch. > > On Fri, Dec 19, 2014 at 06:49:29PM +0800, Chao Yu wrote: > > Now f2fs have page-block mapping cache which can cache only one extent mapping > > between contiguous logical address and physical address. > > Normally, this design will work well because f2fs will expand coverage area of > > the mapping extent when we write forward sequentially. But when we write data > > randomly in Out-Place-Update mode, the extent will be shorten and hardly be > > expanded for most time as following reasons: > > 1.The short part of extent will be discarded if we break contiguous mapping in > > the middle of extent. > > 2.The new mapping will be added into mapping cache only at head or tail of the > > extent. > > 3.We will drop the extent cache when the extent became very fragmented. > > 4.We will not update the extent with mapping which we get from readpages or > > readpage. > > > > To solve above problems, this patch adds extent cache base on rb-tree like other > > filesystems (e.g.: ext4/btrfs) in f2fs. By this way, f2fs can support another > > more effective cache between dnode page cache and disk. It will supply high hit > > ratio in the cache with fewer memory when dnode page cache are reclaimed in > > environment of low memory. > > > > Todo: > > *introduce mount option for extent cache. > > *add shrink ability for extent cache. > > > > Signed-off-by: Chao Yu <chao2.yu@samsung.com>
[snip]
> > +static void __try_merge_extent(struct inode *inode, struct extent_info *ei) > > +{ > > + struct rb_root *root = &F2FS_I(inode)->ei_tree.root; > > + struct extent_info *pei = NULL; > > + struct rb_node *node; > > + > > + node = rb_prev(&ei->rb_node); > > + if (node) { > > + pei = rb_entry(node, struct extent_info, rb_node); > > + if (ei->blk == pei->blk + pei->len) { > > Shouldn't we check below together, too? > if (ei->fofs == pei->fofs + pei->len)
Yes, you're right. The following "if (ei->blk + 1 == pei->blk)" has the same problem. I will fix this issue, thanks for your review!
Regards, Yu
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