Re: [PATCH] mm: add MM_SWAPENTS and page table when calculate tasksize in lowmem_scan()

[Xishi Qiu]

On 2016/2/18 15:55, Figo.zhang wrote:

> 
> 
> 2016-02-17 8:35 GMT+08:00 David Rientjes <rientjes@xxxxxxxxxx <mailto:rientjes@xxxxxxxxxx>>:
> 
>     On Tue, 16 Feb 2016, Greg Kroah-Hartman wrote:
> 
>     > On Tue, Feb 16, 2016 at 05:37:05PM +0800, Xishi Qiu wrote:
>     > > Currently tasksize in lowmem_scan() only calculate rss, and not include swap.
>     > > But usually smart phones enable zram, so swap space actually use ram.
>     >
>     > Yes, but does that matter for this type of calculation?  I need an ack
>     > from the android team before I could ever take such a core change to
>     > this code...
>     >
> 
>     The calculation proposed in this patch is the same as the generic oom
>     killer, it's an estimate of the amount of memory that will be freed if it
>     is killed and can exit.  This is better than simply get_mm_rss().
> 
>     However, I think we seriously need to re-consider the implementation of
>     the lowmem killer entirely.  It currently abuses the use of TIF_MEMDIE,
>     which should ideally only be set for one thread on the system since it
>     allows unbounded access to global memory reserves.
> 
> 
> 
> i don't understand why it need wait 1 second:
> 

Hi David,

How about kill more processes at one time?

Usually loading camera will alloc 300-500M memory immediately, so call lmk
repeatedly is a waste of time.

And can we reclaim memory at one time instead of reclaim-alloc-reclaim-alloc...
in this situation? e.g. use try_to_free_pages(), set nr_to_reclaim=300M

Thanks,
Xishi Qiu

> if (test_tsk_thread_flag(p, TIF_MEMDIE) &&
>    time_before_eq(jiffies, lowmem_deathpending_timeout)) {
> task_unlock(p);
> rcu_read_unlock();
> return 0;                             <= why return rather than continue?
> }
> 
> and it will retry and wait many CPU times if one task holding the TIF_MEMDI.
>    shrink_slab_node()   
>        while()
>            shrinker->scan_objects();
>                      lowmem_scan()
>                                  if (test_tsk_thread_flag(p, TIF_MEMDIE) &&
>                                        time_before_eq(jiffies, lowmem_deathpending_timeout)) 
> 
>  
> 
>