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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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 this
> 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 at boot).

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