On Tue, Sep 28, 2010 at 02:44:40PM +0200, Avi Kivity wrote: > On 09/27/2010 09:09 PM, Nathan Fontenot wrote: > >This set of patches decouples the concept that a single memory > >section corresponds to a single directory in > >/sys/devices/system/memory/. On systems > >with large amounts of memory (1+ TB) there are perfomance issues > >related to creating the large number of sysfs directories. For > >a powerpc machine with 1 TB of memory we are creating 63,000+ > >directories. This is resulting in boot times of around 45-50 > >minutes for systems with 1 TB of memory and 8 hours for systems > >with 2 TB of memory. With this patch set applied I am now seeing > >boot times of 5 minutes or less. > > > >The root of this issue is in sysfs directory creation. Every time > >a directory is created a string compare is done against all sibling > >directories to ensure we do not create duplicates. The list of > >directory nodes in sysfs is kept as an unsorted list which results > >in this being an exponentially longer operation as the number of > >directories are created. > > > >The solution solved by this patch set is to allow a single > >directory in sysfs to span multiple memory sections. This is > >controlled by an optional architecturally defined function > >memory_block_size_bytes(). The default definition of this > >routine returns a memory block size equal to the memory section > >size. This maintains the current layout of sysfs memory > >directories as it appears to userspace to remain the same as it > >is today. > > > > Why not update sysfs directory creation to be fast, for example by > using an rbtree instead of a linked list. This fixes an > implementation problem in the kernel instead of working around it > and creating a new ABI. Because the old ABI creates 129,000+ entries inside /sys/devices/system/memory with their associated links from /sys/devices/system/node/node*/ back to those directory entries. Thankfully things like rpm, hald, and other miscellaneous commands scan that information. On our 8 TB test machine, hald runs continuously following boot for nearly an hour mostly scanning useless information from /sys/ Robin > > New ABIs mean old tools won't work, and new tools need to understand > both ABIs. > > -- > error compiling committee.c: too many arguments to function > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- 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>