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On Tue, 18 Mar 2008 15:18:28 +0100 Andi Kleen <andi@firstfloor.org> wrote: > On Tue, Mar 18, 2008 at 12:36:20AM -0700, Andrew Morton wrote: > > On Tue, 18 Mar 2008 02:09:34 +0100 (CET) Andi Kleen <andi@firstfloor.org> wrote: > > > > > This patchkit is an experimental optimization I played around with > > > some time ago. > > > > > > This is more a prototype still, but I wanted to push it out > > > so that other people can play with it. > > > > > > The basic idea is that most programs have the same working set > > > over multiple runs. So instead of demand paging all the text pages > > > in the order the program runs save the working set to disk and prefetch > > > it at program start and then save it at program exit. > > > > > > This allows some optimizations: > > > - it can avoid unnecessary disk seeks because the blocks will be fetched in > > > sorted offset order instead of program execution order. > > > - batch kernel entries (each demand page exception has some > > > overhead just for entering the kernel). This keeps the caches hot too. > > > - The prefetch could be in theory done in the background while the program > > > runs (although that is not implemented currently) > > > > Should be worthwhile for some things. > > > > > Some details on the implementation: > > > > Can't this all be done in userspace? Hook into exit() with an LD_PRELOAD, > > In theory yes, but it would have much more overhead. s/much/slightly/. The main win will be in optimising disk patterns. We can fault in cached pages at, what? A few GB/sec? > Also I think prefetching > algorithms like this really belong in the kernel. hrmph. > > > - Executable files have to be writable by the user executing it > > > currently to get bitmap updates. It would be possible to let the > > > kernel bypass this, but I haven't thought too much about the security > > > implications of it. > > > However any user can use the bitmap data written by a user with > > > write rights. > > > > Those all get fixed with the userspace version? > > No in fact the permission problem is much harder to fix in user space. What's the permission problem? executable-but-not-readable files? Could be handled by passing your request to a suitable-privileged server process, I guess. -- 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/ | |||||||||
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