On Thu, 23 Jul 2020 10:49:02 +0900 js1304@gmail.com wrote:
From: Joonsoo Kim iamjoonsoo.kim@lge.com
Currently, memalloc_nocma_{save/restore} API that prevents CMA area in page allocation is implemented by using current_gfp_context(). However, there are two problems of this implementation.
First, this doesn't work for allocation fastpath. In the fastpath, original gfp_mask is used since current_gfp_context() is introduced in order to control reclaim and it is on slowpath. So, CMA area can be allocated through the allocation fastpath even if memalloc_nocma_{save/restore} APIs are used.
Whoops.
Currently, there is just one user for these APIs and it has a fallback method to prevent actual problem.
Shouldn't the patch remove the fallback method?
Second, clearing __GFP_MOVABLE in current_gfp_context() has a side effect to exclude the memory on the ZONE_MOVABLE for allocation target.
More whoops.
Could we please have a description of the end-user-visible effects of this change? Very much needed when proposing a -stable backport, I think.
d7fefcc8de9147c is over a year old. Why did we only just discover this? This makes one wonder how serious those end-user-visible effects are?
To fix these problems, this patch changes the implementation to exclude CMA area in page allocation. Main point of this change is using the alloc_flags. alloc_flags is mainly used to control allocation so it fits for excluding CMA area in allocation.