Hi Huang, On Tue, Jan 03, 2017 at 01:43:43PM +0800, Huang, Ying wrote: > Hi, Minchan, > > Minchan Kim <minc...@kernel.org> writes: > > > Hi Jan, > > > > On Mon, Jan 02, 2017 at 04:48:41PM +0100, Jan Kara wrote: > >> Hi, > >> > >> On Tue 27-12-16 16:45:03, Minchan Kim wrote: > >> > > Patch 3 splits the swap cache radix tree into 64MB chunks, reducing > >> > > the rate that we have to contende for the radix tree. > >> > > >> > To me, it's rather hacky. I think it might be common problem for page > >> > cache > >> > so can we think another generalized way like range_lock? Ccing Jan. > >> > >> I agree on the hackyness of the patch and that page cache would suffer with > >> the same contention (although the files are usually smaller than swap so it > >> would not be that visible I guess). But I don't see how range lock would > >> help here - we need to serialize modifications of the tree structure itself > >> and that is difficult to achieve with the range lock. So what you would > >> need is either a different data structure for tracking swap cache entries > >> or a finer grained locking of the radix tree. > > > > Thanks for the comment, Jan. > > > > I think there are more general options. One is to shrink batching pages like > > Mel and Tim had approached. > > > > https://patchwork.kernel.org/patch/9008421/ > > https://patchwork.kernel.org/patch/9322793/ > > This helps to reduce the lock contention on radix tree of swap cache. > But splitting swap cache has much better performance. So we switched > from that solution to current solution. > > > Or concurrent page cache by peter. > > > > https://www.kernel.org/doc/ols/2007/ols2007v2-pages-311-318.pdf > > I think this is good, it helps swap and file cache. But I don't know > whether other people want to go this way and how much effort will be > needed. > > In contrast, splitting swap cache is quite simple, for implementation > and review. And the effect is good.
I think general approach is better but I don't want to be a a party pooper if every people are okay with this. I just wanted to point out we need to consider more general approach and I did my best. Decision depends on you guys. Thanks.
