On Tue, Dec 23, 2014 at 05:35:11PM +0800, Chao Yu wrote: > Hi Changman, > > > -----Original Message----- > > From: Changman Lee [mailto:cm224....@samsung.com] > > Sent: Tuesday, December 23, 2014 12:31 PM > > To: Chao Yu > > Cc: 'Jaegeuk Kim'; linux-f2fs-de...@lists.sourceforge.net; > > linux-kernel@vger.kernel.org > > Subject: Re: [RFC PATCH] f2fs: add extent cache base on rb-tree > > > > Hi, > > > > On Mon, Dec 22, 2014 at 03:10:30PM +0800, Chao Yu wrote: > > > Hi Changman, > > > > > > > -----Original Message----- > > > > From: Changman Lee [mailto:cm224....@samsung.com] > > > > Sent: Monday, December 22, 2014 10:03 AM > > > > To: Chao Yu > > > > Cc: Jaegeuk Kim; linux-f2fs-de...@lists.sourceforge.net; > > > > linux-kernel@vger.kernel.org > > > > Subject: Re: [RFC PATCH] f2fs: add extent cache base on rb-tree > > > > > > > > Hi Yu, > > > > > > > > Good approach. > > > > > > Thank you. :) > > > > > > > As you know, however, f2fs breaks extent itself due to COW. > > > > > > Yes, and sometimes f2fs use IPU when override writing, in this condition, > > > by using this approach we can cache more contiguous mapping extent for > > > better > > > performance. > > > > > > > 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. > > > > > > Agree, the more number of extents are growing in one inode, the more > > > memory > > > pressure and longer latency operating in rb-tree we are facing. > > > IMO, to solve this problem, we'd better to add limitation or shrink > > > ability into > > > extent cache: > > > 1.limit extent number per inode with the value set from sysfs and discard > > > extent > > > from inode's extent lru list if we touch the limitation; (e.g. in FAT, > > > max number > > > of mapping extent per inode is fixed: 8) > > > 2.add all extents of inodes into a global lru list, we will try to shrink > > > this list > > > if we're facing memory pressure. > > > > > > How do you think? or any better ideas are welcome. :) > > > > > > > I think both of them are considerable options. > > How about adding extent to inode selected by user using ioctl or xattr? > > In the case of read most files having large size, user could get a benefit > > surely although they are seperated some pieces. > > Yes, I agree, I prefer ioctl more than xattr, as xattr will take over some > extra > space of inode, and also new added xattr name may conflict with exist extent > xattr. > > Anyway, this will provide more flexible management of extent cache to users > of f2fs.
Oh, well. This is not a good way, since we cannot guide users to call another system call for their files. Instead, it needs to check fadvise hints or RDONLY in the open flag? Thanks, > > Thank you for your idea! > > Regards, > Yu > > > > > Thanks, > > > > > > > > > > Anyway, mount option could be alternative for this patch. > > > > > > Yes, will do. > > > > > > Thanks, > > > Yu > > > > > > > > > > > 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...@samsung.com> > > > > > --- > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
