On Tue, Sep 24, 2013 at 08:57:30PM +0800, Jeff Liu wrote: > On 09/24/2013 07:56 AM, Dave Chinner wrote: > > > On Mon, Sep 23, 2013 at 12:47:23PM +0800, Jeff Liu wrote: > >> Hi Dave, > >> > >> On 09/23/2013 08:56 AM, Dave Chinner wrote: > >> > >>> On Sun, Sep 22, 2013 at 04:25:15PM +0800, Jeff Liu wrote: > >>>> From: Jie Liu <jeff.liu@xxxxxxxxxx> > >>>> > >>>> At xfs_iext_realloc_direct(), the new_size is changed by adding > >>>> if_bytes if originally the extent records are stored at the inline > >>>> extent buffer, and we have to switch from it to a direct extent > >>>> list for those new allocated extents, this is wrong. e.g, .... > >> Actually, what I want to say is that we don't need to perform > >> "new_size += ifp->if_bytes;" again at xfs_iext_realloc_direct() > >> because the new_size at xfs_iext_add() already be the size of > >> extents after adding, just as the variable comments is mentioned. > > > > Yes, I understand. > > > > What I'm really asking is that whether there is any specific impact > > you can measure as a result of changing the initial allocation size? > > i.e. are there workloads where there is a measurable difference in > > memory footprint or noticable performance impact of having to > > reallocate the direct array more frequently as files grow and/or > > shrink? > > Not yet observed any performance matter, but IMO this problem can cause > difference in dynamic memory footprint for creating a large number of > files with 3 extents and with additional kmalloc/kfree overhead for 4 > extents file. > > For the first case, the current code will allocate buffers from > kmalloc-128 slab cache rather than kmalloc-64, hence it would occupy > more memory until being dropped from the cache, e.g, > > # Create 10240 files with 3 extents > for ((i=0; i<10240; i++)) > do > xfs_io -f -c 'truncate 10m' /xfs/test_$i > xfs_io -c 'pwrite 0 1' /xfs/test_$i 2>&1 >>/dev/null > xfs_io -c 'pwrite 1m 1' /xfs/test_$i 2>&1 >>/dev/null > xfs_io -c 'pwrite 5m 1' /xfs/test_$i 2>&1 >>/dev/null > done > > # cat /proc/slab_info > # name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab>... > > # Non-patched -- before creating files > kmalloc-128 5391 6176 128 32 1 > kmalloc-64 21852 25152 64 64 1 > > # After that -- the number of objects in 128 slab increased significantly, while > there basically no change in 64 slab > kmalloc-128 15381 15488 128 32 1 > kmalloc-64 21958 25088 64 64 1 > > > # patched -- before creating files > kmalloc-128 5751 7072 128 32 1 > kmalloc-64 21420 24896 64 64 1 > > After after > kmalloc-128 6155 6688 128 32 1 > kmalloc-64 30464 30464 64 64 1 > > With this patch, we can reduce the memory footprint for this particular scenario. Ok, so it's used the kmalloc-64 slab much more effectively and not touched the kmalloc-128 slab. Ok, so thats a measurable difference ;) > > For the 2nd case, i.e, 4 extents file. It need to resize the direct extent list > to add the fourth extent because rnew_bytes is be re-initialized to 64 at the > beginning of xfs_iext_realloc_direct(), however the ifp->if_real_bytes is 128... ... > # The number of kmalloc calls > Default Patched > 110364 103471 And that demonstrates the impact in that the array is downsized as the array grows. Ok, I'm convinced there is a net win here :) Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx> -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
