Re: [PATCHv2 3/7] mm/memblock: introduce allocation boundary for tracing purpose

[Pingfan Liu <kernelfans@gmail.com>]

On Mon, Jan 14, 2019 at 4:50 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> On Mon, Jan 14, 2019 at 04:33:50PM +0800, Pingfan Liu wrote:
> > On Mon, Jan 14, 2019 at 3:51 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
> > >
> > > Hi Pingfan,
> > >
> > > On Fri, Jan 11, 2019 at 01:12:53PM +0800, Pingfan Liu wrote:
> > > > During boot time, there is requirement to tell whether a series of func
> > > > call will consume memory or not. For some reason, a temporary memory
> > > > resource can be loan to those func through memblock allocator, but at a
> > > > check point, all of the loan memory should be turned back.
> > > > A typical using style:
> > > >  -1. find a usable range by memblock_find_in_range(), said, [A,B]
> > > >  -2. before calling a series of func, memblock_set_current_limit(A,B,true)
> > > >  -3. call funcs
> > > >  -4. memblock_find_in_range(A,B,B-A,1), if failed, then some memory is not
> > > >      turned back.
> > > >  -5. reset the original limit
> > > >
> > > > E.g. in the case of hotmovable memory, some acpi routines should be called,
> > > > and they are not allowed to own some movable memory. Although at present
> > > > these functions do not consume memory, but later, if changed without
> > > > awareness, they may do. With the above method, the allocation can be
> > > > detected, and pr_warn() to ask people to resolve it.
> > >
> > > To ensure there were that a sequence of function calls didn't create new
> > > memblock allocations you can simply check the number of the reserved
> > > regions before and after that sequence.
> > >
> > Yes, thank you point out it.
> >
> > > Still, I'm not sure it would be practical to try tracking what code that's called
> > > from x86::setup_arch() did memory allocation.
> > > Probably a better approach is to verify no memory ended up in the movable
> > > areas after their extents are known.
> > >
> > It is a probability problem whether allocated memory sit on hotmovable
> > memory or not. And if warning based on the verification, then it is
> > also a probability problem and maybe we will miss it.
>
> I'm not sure I'm following you here.
>
> After the hotmovable memory configuration is detected it is possible to
> traverse reserved memblock areas and warn if some of them reside in the
> hotmovable memory.
>
Oh, sorry that I did not explain it accurately. Let use say a machine
with nodeA/B/C from low to high memory address. With top-down
allocation by default, at this point, memory will always be allocated
from nodeC. But it depends on machine whether nodeC is hotmovable or
not. The verification can pass on a machine with unmovable nodeC , but
fails on a machine with movable nodeC. It will be a probability issue.

Thanks

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