Hi, On Mon, 2012-11-05 at 19:46 +0800, Zhi Yong Wu wrote: > On Mon, Nov 5, 2012 at 6:33 PM, Steven Whitehouse <swhiteho@xxxxxxxxxx> wrote: > > Hi, > > > > On Mon, 2012-11-05 at 16:44 +0800, Zhi Yong Wu wrote: > >> On Mon, Nov 5, 2012 at 4:28 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > >> > On Mon, Nov 05, 2012 at 10:35:50AM +0800, Zhi Yong Wu wrote: > >> >> On Sat, Nov 3, 2012 at 5:27 AM, Mingming.cao <cmm@xxxxxxxxxx> wrote: > >> >> > On Fri, 2012-11-02 at 14:38 +0800, Zhi Yong Wu wrote: > >> >> >> Here also has another question. > >> >> >> > >> >> >> How to save the file temperature among the umount to be able to > >> >> >> preserve the file tempreture after reboot? > >> >> >> > >> >> >> This above is the requirement from DB product. > >> >> >> I thought that we can save file temperature in its inode struct, that > >> >> >> is, add one new field in struct inode, then this info will be written > >> >> >> to disk with inode. > >> >> >> > >> >> >> Any comments or ideas are appreciated, thanks. > >> >> >> > >> >> >> > >> >> > > >> >> > Maybe could save the last file temperature with extended attributes. > >> >> It seems that only ext4 has the concept of extended attributes. > >> > > >> > All major filesystems have xattr support. They are used extensively > >> > by the security and integrity subsystems, for example. > >> got it, thanks. > >> > > >> > Saving the information might be something that is useful to certian > >> > applications, but lets have the people that need that functionality > >> > spell out their requirements before discussing how or what to > >> > implement. Indeed, discussion shoul dreally focus on getting the > >> > core, in-memory infrastructure sorted out first before trying to > >> > expand the functionality further... > >> ah, but the latest patchset need some love from experienced FS guys:)....... > > > > There is one other possible issue with saving the data into the > > filesystem, which is that it may disturb what you are trying to measure. > > Some filesystems (GFS2 is one) store data for small inodes in the same > > block as the inode itself. So that means the accesses to the saved hot > > tracking info may potentially affect the data access times too. Also > > there is a very limited amount of space to expand the number of fields > > in the inode, so xattr may be the only solution, depending on how much > > data needs to be stored in each case. > Very good analysis, two possible issues are very meanful, thanks. > > > > In the GFS2 case (I don't think it is unique in this) xattrs are stored > > out of line and having to access them in every open means an extra block > > read per inode, which again has performance implications. > > > > So that is not an insurmountable problem, but something to take into > > account in selecting a solution, > In summary, you look like preferring to xattr as its solution. > Well, that depends on exactly how large the data to be stored is, and other factors. It will add overhead to the storage/retrieval but at least it is fairly generic (wrt on-disk format) so likely to be easier to retrofit to existing filesystems. I suspect this may be one of those cases where there is no obvious right answer and it is a case of selecting the least worst option, if that makes sense? Steve. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
