> On Thu, 14 Jun 2007 15:22:46 -0700 (PDT) Christoph Lameter <[EMAIL > PROTECTED]> wrote: > On Thu, 14 Jun 2007, Andrew Morton wrote: > > > With 64k pagesize the amount of memory required to hold a kernel tree (say) > > will go from 270MB to 1400MB. This is not an optimisation. > > I do not think that the 100% users will do kernel compiles all day like > we do. We likely would prefer 4k page size for our small text files.
There are many, many applications which use small files. > > Several 64k pagesize people have already spent time looking at various > > tail-packing schemes to get around this serious problem. And that's on > > _server_ class machines. Large ones. I don't think > > laptop/desktop/samll-server machines would want to go anywhere near this. > > I never understood the point of that exercise. If you have variable page > size then the 64k page size can be used specific to files that benefit > from it. Typically usage scenarios are video audio streaming I/O, large > picture files, large documents with embedded images. These are the major > usage scenarioes today and we suck the. Our DVD/CD subsystems are > currently not capable of directly reading from these devices into the page > cache since they do not do I/O in 4k chunks. So with sufficient magical kernel heuristics or operator intervention, some people will gain some benefit from 64k pagesize. Most people with most workloads will remain where they are: shoving zillions of physically discontiguous pages into fixed-size sg lists. Whereas with contig-pagecache, all users on all machines with all workloads will benefit from the improved merging. > > > fsck times etc etc are becoming an issue for desktop > > > systems > > > > I don't see what fsck has to do with it. > > > > fsck is single-threaded (hence no locking issues) and operates against the > > blockdev pagecache and does a _lot_ of small reads (indirect blocks, > > especially). If the memory consumption for each 4k read jumps to 64k, fsck > > is likely to slow down due to performing a lot more additional IO and due > > to entering page reclaim much earlier. > > Every 64k block contains more information and the number of pages managed > is reduced by a factor of 16. Less seeks , less tlb pressure , less reads, > more cpu cache and cpu cache prefetch friendly behavior. argh. Everything you say is just wrong. A fsck involves zillions of discontiguous small reads. It is largely seek-bound, so there is no benefit to be had here. Your proposed change will introduce regressions by causing larger amounts of physical reading and large amounts of memory consumption. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
