On Tue, Feb 24, 2015 at 01:26:03PM -0500, David Miller wrote: > From: Thomas Graf <tgraf@xxxxxxx> > Date: Tue, 24 Feb 2015 17:50:14 +0000 > > > On 02/24/15 at 12:09pm, David Miller wrote: > >> Thinking about this, if inserts occur during a pending resize, if the > >> nelems of the table has exceeded even the grow threshold for the new > >> table, it makes no sense to allow these async inserts as they are > >> going to make the resize take longer and prolong the pain. > > > > Let's say we start with an initial table size of 16K (we can make > > this system memory depenend) and we grow by 8x. New inserts go > > into the new table immediately so as soon as we have 12K entries > > we'll grow right to 128K buckets. As we grow above 75K we'll start > > growing to 1024K buckets. New entries already go to the 1024K > > buckets at this point given that the first grow cycle should be > > fast. The 2nd grow cycle would take an est 6 RCU grace periods. > > This would also still give us a max of 8K bucket locks which > > should be good enough as well. > > Actually, first of all, let's not start with larger tables. > > The network namespace folks showed clearly that hash tables > are detrimental to per-ns memory costs. So they definitely > want us to start with extremely small tables. Agreed; ideally, the initial table size would just use a single page for the array of bucket heads, which would give 1024 buckets on 32-bit systems or 512 on 64-bit systems. That's more than enough for many client systems, and for many single-application network namespaces. > But once we know something is actively used, sure, increase > the table grow rate as a response to demand. > > So how feasible is it to grow by 4x, 8x, or other powers of > two in one resize operation? Quite feasible. Actually, any integer multiple works fine, though I think a power of two makes sense. I'd suggest trying 4x with the same workloads that had an issue at 2x, and seeing how that goes. - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
