Re: [RFC][PATCH] avoid swapping out with swappiness==0

[KOSAKI Motohiro]

2012/3/30 Satoru Moriya <satoru.moriya@xxxxxxx>:
> Hello Kosaki-san,
>
> On 03/07/2012 01:18 PM, Satoru Moriya wrote:
>> On 03/07/2012 12:19 PM, KOSAKI Motohiro wrote:
>>> Thank you. I brought back to memory it. Unfortunately DB folks are
>>> still mainly using RHEL5 generation distros. At that time,
>>> swapiness=0 doesn't mean disabling swap.
>>>
>>> They want, "don't swap as far as kernel has any file cache page". but
>>> linux don't have such feature. then they used swappiness for emulate
>>> it. So, I think this patch clearly make userland harm. Because of, we
>>> don't have an alternative way.
>
> As I wrote in the previous mail(see below), with this patch
> the kernel begins to swap out when the sum of free pages and
> filebacked pages reduces less than watermark_high.
>
> So the kernel reclaims pages like following.
>
> nr_free + nr_filebacked >= watermark_high: reclaim only filebacked pages
> nr_free + nr_filebacked <  watermark_high: reclaim only anonymous pages

How?
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