On Sat, Oct 7, 2023 at 5:17 AM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, 11 May 2023 13:22:30 +0800 "zhaoyang.huang" <zhaoyang.huang@xxxxxxxxxx> wrote: > > > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> > > > > Let us look at the timeline of scenarios below with WMARK_LOW=25MB WMARK_MIN=5MB > > (managed pages 1.9GB). We can find that CMA begin to be used until 'C' under the > > method of 'fixed 2 times of free cma over free pages' which could have the > > scenario 'A' and 'B' into a fault state, that is, free UNMOVABLE & RECLAIMABLE > > pages is lower than corresponding watermark without reclaiming which should be > > deemed as against current memory policy. This commit try to solve this by > > checking zone_watermark_ok again with removing CMA pages which could lead to a > > proper time point of CMA's utilization. > > > > -- Free_pages > > | > > | > > -- WMARK_LOW > > | > > -- Free_CMA > > | > > | > > -- > > > > Free_CMA/Free_pages(MB) A(12/30) --> B(12/25) --> C(12/20) > > fixed 1/2 ratio N N Y > > this commit Y Y Y > > > > Roman previously asked > > : Also I'm a bit concerned about potential performance implications. > : Would be great to provide some benchmarks or some data. Probably it's > : ok because of we have pcp caches on top, but I'm not 100% sure. > > Are you able to perform such testing and tell us the result? I have applied this patch in a v5.4 based ANDROID system and got no regression problem. Actually, this commit is aimed to have alloc_pages(GFP_USER) use CMA instead of stealing U&R(could lead to GFP_KERNEL fail) only when zone's free pages and free cma are around WATERMARK_LOW/MIN which would NOT affect most scenarios. > > Thanks. >
