Messages in this thread | | | Date | Sat, 29 Sep 2007 12:56:55 +0300 | From | Artem Bityutskiy <> | Subject | Re: Write-back from inside FS - need suggestions |
| |
Andrew Morton wrote: > This is precisely the problem which needs to be solved for delayed > allocation on ext2/3/4. This is because it is infeasible to work out how > much disk space an ext2 pagecache page will take to write out (it will > require zero to three indirect blocks as well). > > When I did delalloc-for-ext2, umm, six years ago I did > maximally-pessimistic in-memory space accounting and I think I just ran a > superblock-wide sync operation when ENOSPC was about to happen. That > caused all the pessimistic reservations to be collapsed into real ones, > releasing space. So as the disk neared a real ENOSPC, the syncs becaome > more frequent. But the overhead was small. > > I expect that a similar thing was done in the ext4 delayed allocation > patches - you should take a look at that and see what can be > shared/generalised/etc. > > ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/ext4-patches/LATEST/broken-out/ > > Although, judging by the comment in here: > > ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/ext4-patches/LATEST/broken-out/ext4-delayed-allocation.patch > > + * TODO: > + * MUST: > + * - flush dirty pages in -ENOSPC case in order to free reserved blocks > > things need a bit more work. Hopefully that's a dead comment. > > <looks> > > omigod, that thing has gone and done a clone-and-own on half the VFS. > Anyway, I doubt if you'll be able to find a design description anyway > but you should spend some time picking it apart. It is the same problem..
(For some reasons I haven't got your answer in my mailbox, found it in archives)
Thank you for these pointers. I was looking at ext4 code and found haven't found what they do in these cases. I think I need some hints to realize what's going on there. Our FS is so different from traditional ones - e.g., we do not use buffer heads, we do not have block device underneath, etc, so I even doubt I can borrow anything from ext4.
I have impression that I just have to implement my own list of inodes and my own victim-picking policies. Although I still think it should better be done on VFS level, because it has all these LRU lists, and I'd duplicate things.
Nevertheless, I add Teo on CC in a hope he'll give me some pointers.
-- Best Regards, Artem Bityutskiy (Артём Битюцкий) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |