RE: [Xen-devel] is paging_new_log_dirty_page alloc page harmfull?

[MaoXiaoyun <tinnycloud@xxxxxxxxxxx>]

Thank stefano.
 
It looks like free_mem_slack_kb refer to dom0, right?
 
But, in my situation, since I use a balloond to management the memory resources
between all domains(except dom0, for performance consideration), it is possible
all memory is given to domU, which will cause some unexpect problems.
 
So am ask is there a considerable memory amout need to be reserved for Xen itself.
thanks. 

 
> Date: Mon, 7 Mar 2011 16:16:55 +0000
> From: stefano.stabellini@xxxxxxxxxxxxx
> To: Tim.Deegan@xxxxxxxxxxxxx
> CC: tinnycloud@xxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxx; Stefano.Stabellini@xxxxxxxxxxxxx
> Subject: Re: [Xen-devel] is paging_new_log_dirty_page alloc page harmfull?
>
> On Mon, 7 Mar 2011, Tim Deegan wrote:
> > At 03:41 +0000 on 07 Mar (1299469316), MaoXiaoyun wrote:
> > > Thanks Tim.
> > >
> > > Do you have suggestion on how many memory I should reserved, is 512M
> > > enough? There is a balloon daemon process in dom0 do the memory
> > > management, the striaght way to reserve memory is after recycle memory
> > > form domains which no need memory , then give the memory to those
> > > domains who need memory. What do you think of this?
> >
> > Maybe the people who have been working on the toolstack can answer th is
> > one - 512MiB free sounds like more than enough to me but I could be
> > wrong.
>
> give a look at how freememslack is set in
> tools/libxl/libxl.c:libxl__fill_dom0_memory_info:
>
> free_mem_slack_kb = (uint32_t) (PAGE_TO_MEMKB(physinfo.total_pages) -
> info.current_memkb);
> /* From empirical measurements the free_mem_slack shouldn't be more
> * than 15% of the total memory present on the system. */
> if (free_mem_slack_kb > PAGE_TO_MEMKB(physinfo.total_pages) * 0.15)
> free_mem_slack_kb = PAGE_TO_MEMKB(physinfo.total_pages) * 0.15;
> libxl__xs_write(gc, t, free_mem_slack_path, "%"PRIu32, free_mem_slack_kb);
>
> the memory left free in the system is never more than 15% of the total
> memory available and is calculated as the difference between
> physinfo.total_pages (total pages in the system) and info.current_memkb
> (memory currently used by dom0 a t boot).

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