On 11/17/2016 11:11 PM, David Rientjes wrote: > On Thu, 17 Nov 2016, Vlastimil Babka wrote: > >>> The total number of free pages is still tracked, however, to not make >>> zone_watermark_ok() more expensive. Reading /proc/pagetypeinfo, however, >>> is faster. >> >> Yeah I've already seen a case with /proc/pagetypeinfo causing soft >> lockups due to high number of iterations... >> > > Thanks for taking a look at the patchset! > > Wow, I haven't seen /proc/pagetypeinfo soft lockups yet, I thought this > was a relatively minor point :) Well to be honest, it was a system misconfigured with numa=off which made the lists both longer and more numa-distant. But nevertheless, we might get there. It's not nice when userspace can so easily trigger long iterations under the zone/node lock... > But it looks like we need some > improvement in this behavior independent of memory compaction anyway. Yeah. >>> This patch introduces no functional change and increases the amount of >>> per-zone metadata at worst by 48 bytes per memory zone (when CONFIG_CMA >>> and CONFIG_MEMORY_ISOLATION are enabled). >> >> Isn't it 48 bytes per zone and order? >> > > Yes, sorry, I'll fix that in v2. I think less than half a kilobyte for > each memory zone is satisfactory for extra tracking, compaction > improvements, and optimized /proc/pagetypeinfo, though. I'm not worried about memory usage, but perhaps cache usage. >>> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx> >> >> I'd be for this if there are no performance regressions. It affects hot >> paths and increases cache footprint. I think at least some allocator >> intensive microbenchmark should be used. >> > > I can easily implement a test to stress movable page allocations from > fallback MIGRATE_UNMOVABLE pageblocks and freeing back to the same > pageblocks. I assume we're not interested in memory offline benchmarks. I meant just allocation benchmarks to see how much the extra operations and cache footprint matters. > What do you think about the logic presented in patch 2/2? Are you > comfortable with a hard-coded ratio such as 1/64th of free memory or would > you prefer to look at the zone's watermark with the number of free pages > from MIGRATE_MOVABLE pageblocks rather than NR_FREE_PAGES? I was split > between the two options. The second options makes more sense to me intuitively as it resembles what we've been doing until now. Maybe just don't require such a large gap as compaction_suitable does? > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>