RE: [RFC][PATCH] avoid swapping out with swappiness==0
From: Satoru Moriya
Date: Fri Mar 30 2012 - 18:44:54 EST
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
Do you think this behavior satisfies DB users' requirement?
> If they expect the behavior that "don't swap as far as kernel has any
> file cache page", this patch definitely helps them because if we set
> swappiness==0, kernel does not swap out
> *until* nr_free + nr_filebacked < high watermark in the zone.
> It means kernel begins to swap out when nr_free + nr_filebacked
> becomes less than high watermark.
> But, yes, this patch actually changes the behavior with swappiness==0
> and so it may make userland harm.
> How about introducing new value e.g -1 to avoid swap and maintain
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/