Hi Akashi,
On Thu, Nov 17, 2016 at 02:34:24PM +0900, AKASHI Takahiro wrote:
> On Wed, Nov 16, 2016 at 04:30:15PM +0000, Will Deacon wrote:
> > I thought limit was just a physical address, and then
>
> No, it's not.
Quite right, it's a size. Sorry about that.
> > memblock_mem_limit_remove_map operated on the end of the nearest memblock?
>
> No, but "max_addr" returned by __find_max_addr() is a physical address
> and the end address of memory of "limit" size in total.
>
> > You could leave the __find_max_addr call in memblock_mem_limit_remove_map,
> > given that I don't think you need/want it for memblock_cap_memory_range.
> >
> > > So I added an extra argument, exact, to a common function to specify
> > > distinct behaviors. Confusing? Please see the patch below.
> >
> > Oh yikes, this certainly wasn't what I had in mind! My observation was
> > just that memblock_mem_limit_remove_map(limit) does:
> >
> >
> > 1. memblock_isolate_range(limit - limit+ULLONG_MAX)
> > 2. memblock_remove_region(all non-nomap regions in the isolated region)
> > 3. truncate reserved regions to limit
> >
> > and your memblock_cap_memory_range(base, size) does:
> >
> > 1. memblock_isolate_range(base - base+size)
> > 2, memblock_remove_region(all non-nomap regions above and below the
> > isolated region)
> > 3. truncate reserved regions around the isolated region
> >
> > so, assuming we can invert the isolation in one of the cases, then they
> > could share the same underlying implementation.
>
> Please see my simplified patch below which would explain what I meant.
> (Note that the size is calculated by 'max_addr - 0'.)
>
> > I'm probably just missing something here, because the patch you've ended
> > up with is far more involved than I anticipated...
>
> I hope that it will meet almost your anticipation.
It looks much better, thanks! Just one question below.
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 7608bc3..fea1688 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1514,11 +1514,37 @@ void __init memblock_enforce_memory_limit(phys_addr_t limit)
> (phys_addr_t)ULLONG_MAX);
> }
>
> +void __init memblock_cap_memory_range(phys_addr_t base, phys_addr_t size)
> +{
> + int start_rgn, end_rgn;
> + int i, ret;
> +
> + if (!size)
> + return;
> +
> + ret = memblock_isolate_range(&memblock.memory, base, size,
> + &start_rgn, &end_rgn);
> + if (ret)
> + return;
> +
> + /* remove all the MAP regions */
> + for (i = memblock.memory.cnt - 1; i >= end_rgn; i--)
> + if (!memblock_is_nomap(&memblock.memory.regions[i]))
> + memblock_remove_region(&memblock.memory, i);
In the case that we have only one, giant memblock that covers base all
of base + size, can't we end up with start_rgn = end_rgn = 0? In which
case, we'd end up accidentally removing the map regions here.
The existing code:
> - /* remove all the MAP regions above the limit */
> - for (i = end_rgn - 1; i >= start_rgn; i--) {
> - if (!memblock_is_nomap(&type->regions[i]))
> - memblock_remove_region(type, i);
> - }
seems to handle this.
Will
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