Re: [PATCH v2] Revert "mm: skip CMA pages when they are not available"

[Michal Hocko]

On Fri 15-03-24 16:18:03, liuhailong@xxxxxxxx wrote:
> From: "Hailong.Liu" <liuhailong@xxxxxxxx>
> 
> This reverts
> commit b7108d66318a ("Multi-gen LRU: skip CMA pages when they are not eligible")
> commit 5da226dbfce3 ("mm: skip CMA pages when they are not available")
> 
> skip_cma may cause system not responding. if cma pages is large in lru_list
> and system is in lowmemory, many tasks would direct reclaim and waste
> cpu time to isolate_lru_pages and return.
> 
> Test this patch on android-5.15 8G device
> reproducer:
> - cma_declare_contiguous 3G pages
> - set /proc/sys/vm/swappiness 0 to enable direct_reclaim reclaim file
>   only.
> - run a memleak process in userspace

Does this represent a sane configuration? CMA memory is unusable for
kernel allocations and memleak process is also hard to reclaim due to
swap suppression. Isn't such a system doomed to struggle to reclaim any
memory? Btw. how does the same setup behave with the regular LRU
implementation? My guess would be that it would struggle as well.
-- 
Michal Hocko
SUSE Labs