linux-kernel - Re: [PATCH] mm: There should have an unit (kB)

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Date:   Sat, 2 Nov 2019 16:53:09 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>
cc:     hui yang <yanghui.def@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, mhocko@...e.com,
        dan.j.williams@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: There should have an unit (kB)

On Sat, 2 Nov 2019, Matthew Wilcox wrote:

> On Sat, Nov 02, 2019 at 10:18:07PM +0800, hui yang wrote:
> > From: YangHui <yanghui.def@...il.com>
> > 
> > -    printk(KERN_CONT " %ld", zone->lowmem_reserve[i]);
> > +    printk(KERN_CONT " %ldkB", zone->lowmem_reserve[i]);
> > Make it look more perfect
> 
> I don't think this is accounted in kilobytes though.  Isn't it the
> number of pages?
> 

Yes, it's not in KB.

Speaking of lowmem_reserve, however, the current default of 1/256 for both 
ZONE_DMA and ZONE_DMA32 seem too large as memory capacities of nodes 
increase.  We tune this to be much smaller so that we don't have as much 
memory set aside only for GFP_DMA or GFP_DMA32 allocations for that reason 
and because there is less reliance on lowmem for our configurations.

I'm wondering if the default should either be 1/256 up to a bounded memory 
capacity and then the excess is disregarded or whether the default itself 
should be changed to, say, 1024.

Looping in Johannes who may also have an opinion on this.