On Mon, 12 Apr 2010 20:38:29 -0400 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 12 Apr 2010 13:02:34 +0300 Avi Kivity <avi@xxxxxxxxxx> wrote: > > > The only scenario I can see where it degrades is that you have a dcache > > load that spills over to all of memory, then falls back leaving a pinned > > page in every huge frame. It can happen, but I don't see it as a likely > > scenario. But maybe I'm missing something. > > <prehistoric memory> > > This used to happen fairly easily. You have a directory tree and some > app which walks down and across it, stat()ing regular files therein. > So you end up with dentries and inodes which are laid out in memory as > dir-file-file-file-file-...-file-dir-file-... Then the file > dentries/inodes get reclaimed and you're left with a sparse collection > of directory dcache/icache entries - massively fragmented. > > I forget _why_ it happened. Perhaps because S_ISREG cache items aren't > pinned by anything, but S_ISDIR cache items are pinned by their children > so it takes many more expiry rounds to get rid of them. > > There was talk about fixing this, perhaps by using different slab > caches for dirs vs files. Hard, because the type of the file/inode > isn't known at allocation time. Nothing happened about it. Actually I don't think that would be hard at all. ->lookup can return a different dentry than the one passed in, usually using d_splice_alias to find it. So when you create an inode for a directory, create an anonymous dentry, attach it via i_dentry, and it should "just work". That is assuming this is still a "problem" that needs to be "fixed". NeilBrown -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>