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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: [PATCH 5/5] xen: release all pages within 1-1 p2m mappings
On Fri, Aug 19, 2011 at 03:57:20PM +0100, David Vrabel wrote:
> In xen_memory_setup() all reserved regions and gaps are set to an
> identity (1-1) p2m mapping. If an available page has a PFN within one
> of these 1-1 mappings it will become accessible (as it MFN is lost) so
> release them before setting up the mapping.
>
> This can make an additional 256 MiB or more of RAM available
> (depending on the size of the reserved regions in the memory map).
.. if the xen_start_info->nr_pages overlaps the reserved region.
>
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxx>
> ---
> arch/x86/xen/setup.c | 88
> ++++++++++++--------------------------------------
> 1 files changed, 21 insertions(+), 67 deletions(-)
>
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 93e4542..0f1cd69 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -123,73 +123,33 @@ static unsigned long __init
> xen_release_chunk(phys_addr_t start_addr,
> return len;
> }
>
> -static unsigned long __init xen_return_unused_memory(unsigned long max_pfn,
> - const struct e820entry
> *map,
> - int nr_map)
> +static unsigned long __init xen_set_identity_and_release(const struct
> e820entry *list,
> + ssize_t map_size,
> + unsigned long nr_pages)
> {
> - phys_addr_t max_addr = PFN_PHYS(max_pfn);
> - phys_addr_t last_end = ISA_END_ADDRESS;
> + phys_addr_t avail_end = PFN_PHYS(nr_pages);
> + phys_addr_t last_end = 0;
> unsigned long released = 0;
> - int i;
> -
> - /* Free any unused memory above the low 1Mbyte. */
> - for (i = 0; i < nr_map && last_end < max_addr; i++) {
> - phys_addr_t end = map[i].addr;
> - end = min(max_addr, end);
> -
> - if (last_end < end)
> - released += xen_release_chunk(last_end, end);
> - last_end = max(last_end, map[i].addr + map[i].size);
> - }
> -
> - if (last_end < max_addr)
> - released += xen_release_chunk(last_end, max_addr);
> -
> - printk(KERN_INFO "released %lu pages of unused memory\n", released);
> - return released;
> -}
> -
> -static unsigned long __init xen_set_identity(const struct e820entry *list,
> - ssize_t map_size)
> -{
> - phys_addr_t last = xen_initial_domain() ? 0 : ISA_END_ADDRESS;
> - phys_addr_t start_pci = last;
> const struct e820entry *entry;
> - unsigned long identity = 0;
> int i;
>
> for (i = 0, entry = list; i < map_size; i++, entry++) {
> - phys_addr_t start = entry->addr;
> - phys_addr_t end = start + entry->size;
> -
> - if (start < last)
> - start = last;
> + phys_addr_t begin = last_end;
The "begin" is a bit confusing. You are using the previous E820 entry's end -
not
the beginning of this E820 entry. Doing a s/begin/last_end/ makes
the code a bit easier to understand.
> + phys_addr_t end = entry->addr + entry->size;
>
> - if (end <= start)
> - continue;
> + last_end = end;
Please include the comment:
/* This entry end. */
>
> - /* Skip over the 1MB region. */
> - if (last > end)
> - continue;
> + if (entry->type == E820_RAM || entry->type == E820_UNUSABLE)
> + end = entry->addr;
And:
/* Should encapsulate the gap between prev_end and this E820
entry's starting address. */
>
> - if ((entry->type == E820_RAM) || (entry->type ==
> E820_UNUSABLE)) {
> - if (start > start_pci)
> - identity += set_phys_range_identity(
> - PFN_UP(start_pci),
> PFN_DOWN(start));
> + if (begin < end) {
> + if (begin < avail_end)
> + released += xen_release_chunk(begin, min(end,
> avail_end));
>
> - /* Without saving 'last' we would gooble RAM too
> - * at the end of the loop. */
> - last = end;
> - start_pci = end;
> - continue;
> + set_phys_range_identity(PFN_UP(begin), PFN_DOWN(end));
identity += set_phys_range ..
> }
> - start_pci = min(start, start_pci);
> - last = end;
> }
> - if (last > start_pci)
> - identity += set_phys_range_identity(
> - PFN_UP(start_pci), PFN_DOWN(last));
> - return identity;
OK, but you have ripped out the nice printk's that existed before. So add them
back in:
printk(KERN_INFO "released %lu pages of unused memory\n", released);
printk(KERN_INFO "Set %ld page(s) to 1-1 mapping.\n", identity);
as they are quite useful in the field.
> + return released;
> }
>
> static unsigned long __init xen_get_max_pages(void)
> @@ -217,7 +177,6 @@ char * __init xen_memory_setup(void)
> struct xen_memory_map memmap;
> unsigned long max_pages;
> unsigned long extra_pages = 0;
> - unsigned long identity_pages = 0;
> int i;
> int op;
>
> @@ -250,7 +209,12 @@ char * __init xen_memory_setup(void)
> if (max_pages > max_pfn)
> extra_pages += max_pages - max_pfn;
>
> - extra_pages += xen_return_unused_memory(max_pfn, map,
> memmap.nr_entries);
> + /*
> + * Set P2M for all non-RAM pages and E820 gaps to be identity
> + * type PFNs. Any RAM pages that would be made inaccesible by
> + * this are first released.
> + */
> + extra_pages += xen_set_identity_and_release(map, memmap.nr_entries,
> max_pfn);
>
> /*
> * Clamp the amount of extra memory to a EXTRA_MEM_RATIO
> @@ -294,10 +258,6 @@ char * __init xen_memory_setup(void)
> * In domU, the ISA region is normal, usable memory, but we
> * reserve ISA memory anyway because too many things poke
> * about in there.
> - *
> - * In Dom0, the host E820 information can leave gaps in the
> - * ISA range, which would cause us to release those pages. To
> - * avoid this, we unconditionally reserve them here.
> */
> e820_add_region(ISA_START_ADDRESS, ISA_END_ADDRESS - ISA_START_ADDRESS,
> E820_RESERVED);
> @@ -314,12 +274,6 @@ char * __init xen_memory_setup(void)
>
> sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
>
> - /*
> - * Set P2M for all non-RAM pages and E820 gaps to be identity
> - * type PFNs.
> - */
> - identity_pages = xen_set_identity(e820.map, e820.nr_map);
> - printk(KERN_INFO "Set %ld page(s) to 1-1 mapping.\n", identity_pages);
> return "Xen";
> }
>
> --
> 1.7.2.5
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