Michael Rubin wrote: > On Fri, Sep 12, 2008 at 1:18 PM, Andrew Morton > <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: >> One thing to think about please: Michael Rubin is hitting problems with >> the existing /proc/sys/vm/dirty-ratio. Its present granularity of 1% >> is just too coarse for really large machines, and as >> memory-size/disk-speed ratios continue to increase, this will just get >> worse. > > Re-sending since I top-posted before. Never again. Also adding more > thoughts on a byte based interface. > > Currently the problem we are hitting is that we cannot specify pdflush > to have background limits less than 1% of memory. I am currently > finishing up a patch right now that adds a dirty_ratio_millis > interface. I hope to submit the patch to LKML by the end of the week. > > The idea is that we don't want to break backwards compatibility and we > also don't want to have two conflicting knobs in the sysctl or > /proc/sys/vm/ space. I thought adding a new knob for those who want to > specify finer grained functionality was a compromise. So the patch has > a vm_dirty_ratio and a vm_dirty_ratio_millis interface. The first to > specify 0-100% and the second to specify .0 to .999%. > > So to represent 0.125% of RAM we set > vm_dirty_ratio = 0 > vm_dirty_ratio_millis = 125 > > The same for the background_ratio. > > I would also prefer using a bytes interface but I am not sure how to > offer that without either removing the legacy interface of the ratios > or by offering a concurrent interface that might be confusing such as > when users are looking at the old one and not aware of a new one. > > Any feedback? > > mrubin I think using millis is ok today, but it may not scale well to systems with 1TB of memory (in this case the min granularity would be 10MB). A bytes/pages interface would resolve such problem also for tomorrow machines. Moreover, wouldn't it be safer to set them mutually exclusive? I mean, writing a value != 0 to vm_dirty_millis automatically sets vm_dirty_ratio to 0 (disabled) and vice versa (this could be implemented using an appropriate .proc_handler for example). OK, I would like to set percentages like 12.456%, but if we don't do so a simple "sysctl -p" could create unexpected behaviours, reconfiguring the vm_dirty_ratio and not vm_dirty_ratio_millis for example. The same should be valid also for a bytes/pages interface, so setting vm_dirty_bytes != 0 (or vm_dirty_pages) should "disable" vm_dirty_ratio and vice versa. Thanks, -Andrea _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers