Andy and Chris, On Sun, Feb 21, 2010 at 11:02:38AM +0800, Andy Isaacson wrote: > On Tue, Feb 16, 2010 at 10:13:12AM -0800, Chris Frost wrote: > > Add the fincore() system call. fincore() is mincore() for file descriptors. > > > > The functionality of fincore() can be emulated with an mmap(), mincore(), > > and munmap(), but this emulation requires more system calls and requires > > page table modifications. fincore() can provide a significant performance > > improvement for non-sequential in-core queries. > > In addition to being expensive, mmap/mincore/munmap perturb the VM's > eviction algorithm -- a page is less likely to be evicted if it's > mmapped when being considered for eviction. > > I frequently see this happen when using mincore(1) from > http://bitbucket.org/radii/mincore/ -- "watch mincore -v *.big" while > *.big are being sequentially read results in a significant number of > pages remaining in-core, whereas if I only run mincore after the > sequential read is complete, the large files will be nearly-completely > out of core (except for the tail of the last file, of course). > > It's very interesting to watch > % watch --interval=.5 mincore -v * > > while an IO-intensive process is happening, such as mke2fs on a > filesystem image. > > So, I support the addition of fincore(2) and would use it if it were > merged. I'd like to advocate the "pagecache object collections", a ftrace based alternative: http://lkml.org/lkml/2010/2/9/156 Which will provide much more information than fincore(). I'd really appreciate it if you can join and use the general "pagecache object collections" facility. Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
