Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android

[Joel Fernandes]

On Sun, Mar 10, 2019 at 01:34:03PM -0700, Sultan Alsawaf wrote:
[...]
>  
>  	/* Perform scheduler related setup. Assign this task to a CPU. */
>  	retval = sched_fork(clone_flags, p);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3eb01dedf..fd0d697c6 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -67,6 +67,7 @@
>  #include <linux/lockdep.h>
>  #include <linux/nmi.h>
>  #include <linux/psi.h>
> +#include <linux/simple_lmk.h>
>  
>  #include <asm/sections.h>
>  #include <asm/tlbflush.h>
> @@ -967,6 +968,11 @@ static inline void __free_one_page(struct page *page,
>  		}
>  	}
>  
> +#ifdef CONFIG_ANDROID_SIMPLE_LMK
> +	if (simple_lmk_page_in(page, order, migratetype))
> +		return;
> +#endif
> +
>  	list_add(&page->lru, &zone->free_area[order].free_list[migratetype]);
>  out:
>  	zone->free_area[order].nr_free++;
> @@ -4427,6 +4433,13 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	if (costly_order && !(gfp_mask & __GFP_RETRY_MAYFAIL))
>  		goto nopage;
>  
> +#ifdef CONFIG_ANDROID_SIMPLE_LMK
> +	page = simple_lmk_oom_alloc(order, ac->migratetype);
> +	if (page)
> +		prep_new_page(page, order, gfp_mask, alloc_flags);
> +	goto got_pg;
> +#endif
> +

Hacking generic MM code with Android-specific callback is probably a major
issue with your patch. Also I CC'd -mm maintainers and lists since your patch
touches page_alloc.c. Always run get_maintainer.pl before sending a patch. I
added them this time.

Have you looked at the recent PSI work that Suren and Johannes have been
doing [1]?  As I understand, userspace lmkd may be migrated to use that at some
point.  Suren can provide more details. I am sure AOSP contributions to make
LMKd better by using the PSI backend would be appreciated. Please consider
collaborating on that and help out, thanks. Check the cover-letter of that
patch [1] where LMKd is mentioned.

thanks,

 - Joel

[1] https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1951257.html