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SubjectRe: [PATCH] mm: add MM_SWAPENTS and page table when calculate tasksize in lowmem_scan()
On 2016/2/18 15:55, Figo.zhang wrote:

>
>
> 2016-02-17 8:35 GMT+08:00 David Rientjes <rientjes@google.com <mailto:rientjes@google.com>>:
>
> 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))
>
>
>
>


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