Re: [Bug fix PATCH 1/2] acpi, movablemem_map: Exclude memblock.reservedranges when parsing SRAT.

[Will Huck]

On 02/20/2013 08:31 PM, Tang Chen wrote:
> On 02/20/2013 07:00 PM, Tang Chen wrote:
> > As mentioned by HPA before, when we are using movablemem_map=acpi, if 
> > all the
> > memory ranges in SRAT is hotpluggable, then no memory can be used by 
> > kernel.
> >
> > Before parsing SRAT, memblock has already reserve some memory ranges 
> > for other
> > purposes, such as for kernel image, and so on. We cannot prevent 
> > kernel from
> > using these memory. So we need to exclude these ranges even if these 
> > memory is
> > hotpluggable.
> >
> > This patch changes the movablemem_map=acpi option's behavior. The 
> > memory ranges
> > reserved by memblock will not be added into movablemem_map.map[]. So 
> > even if
> > all the memory is hotpluggable, there will always be memory that 
> > could be used
> > by the kernel.

What's the relationship between e820 map and SRAT?

> > Reported-by: H Peter Anvin<hpa@xxxxxxxxx>
> > Signed-off-by: Tang Chen<tangchen@xxxxxxxxxxxxxx>
> > ---
> >   arch/x86/mm/srat.c |   18 +++++++++++++++++-
> >   1 files changed, 17 insertions(+), 1 deletions(-)
> >
> > diff --git a/arch/x86/mm/srat.c b/arch/x86/mm/srat.c
> > index 62ba97b..b8028b2 100644
> > --- a/arch/x86/mm/srat.c
> > +++ b/arch/x86/mm/srat.c
> > @@ -145,7 +145,7 @@ static inline int save_add_info(void) {return 0;}
> >   static void __init
> >   handle_movablemem(int node, u64 start, u64 end, u32 hotpluggable)
> >   {
> > -    int overlap;
> > +    int overlap, i;
> >       unsigned long start_pfn, end_pfn;
> >
> >       start_pfn = PFN_DOWN(start);
> > @@ -161,8 +161,24 @@ handle_movablemem(int node, u64 start, u64 end, 
> > u32 hotpluggable)
> >        *
> >        * Using movablemem_map, we can prevent memblock from 
> > allocating memory
> >        * on ZONE_MOVABLE at boot time.
> > +     *
> > +     * Before parsing SRAT, memblock has already reserve some memory 
> > ranges
> > +     * for other purposes, such as for kernel image. We cannot prevent
> > +     * kernel from using these memory, so we need to exclude these 
> > memory
> > +     * even if it is hotpluggable.
> >        */
> >       if (hotpluggable&&  movablemem_map.acpi) {
> > +        /* Exclude ranges reserved by memblock. */
> > +        struct memblock_type *rgn =&memblock.reserved;
> > +
> > +        for (i = 0; i<  rgn->cnt; i++) {
> > +            if (end<= rgn->regions[i].base ||
> > +                start>= rgn->regions[i].base +
> > +                rgn->regions[i].size)
>
> Hi all,
>
> Here, I scan the memblock.reserved each time we parse an entry because 
> the
> rgn->regions[i].nid is set to MAX_NUMNODES in memblock_reserve(). So I 
> cannot
> obtain the nid which the kernel resides in directly from 
> memblock.reserved.
>
> I think there could be some problems if the memory ranges in SRAT are 
> not in
> increasing order, since if [3,4) [1,2) are all on node0, and kernel is 
> not
> using [3,4), but using [1,2), then I cannot remove [3,4) because I 
> don't know
> on which node [3,4) is.
>
> Any idea for this ?
>
> And by the way, I think this approach works well when the memory 
> entries in
> SRAT are arranged in increasing order.
>
> Thanks. :)
>
> > +                continue;
> > +            goto out;
> > +        }
> > +
> >           insert_movablemem_map(start_pfn, end_pfn);
> >
> >           /*
>
> --
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