Re: [PATCH v2 2/5] mm,memory_hotplug: Introduce MHP_VMEMMAP_FLAGS

[osalvador]

On 2019-07-24 22:11, Dan Williams wrote:
> On Tue, Jun 25, 2019 at 12:53 AM Oscar Salvador <osalvador@xxxxxxx> 
> wrote:
> > This patch introduces MHP_MEMMAP_DEVICE and MHP_MEMMAP_MEMBLOCK flags,
> > and prepares the callers that add memory to take a "flags" parameter.
> > This "flags" parameter will be evaluated later on in Patch#3
> > to init mhp_restrictions struct.
> >
> > The callers are:
> >
> > add_memory
> > __add_memory
> > add_memory_resource
> >
> > Unfortunately, we do not have a single entry point to add memory, as 
> > depending
> > on the requisites of the caller, they want to hook up in different 
> > places,
> > (e.g: Xen reserve_additional_memory()), so we have to spread the 
> > parameter
> > in the three callers.
> >
> > The flags are either MHP_MEMMAP_DEVICE or MHP_MEMMAP_MEMBLOCK, and 
> > only differ
> > in the way they allocate vmemmap pages within the memory blocks.
> >
> > MHP_MEMMAP_MEMBLOCK:
> >         - With this flag, we will allocate vmemmap pages in each 
> > memory block.
> >           This means that if we hot-add a range that spans multiple 
> > memory blocks,
> >           we will use the beginning of each memory block for the 
> > vmemmap pages.
> >           This strategy is good for cases where the caller wants the 
> > flexiblity
> >           to hot-remove memory in a different granularity than when it 
> > was added.
> >
> >           E.g:
> >                 We allocate a range (x,y], that spans 3 memory blocks, 
> > and given
> >                 memory block size = 128MB.
> >                 [memblock#0  ]
> >                 [0 - 511 pfns      ] - vmemmaps for section#0
> >                 [512 - 32767 pfns  ] - normal memory
> >
> >                 [memblock#1 ]
> >                 [32768 - 33279 pfns] - vmemmaps for section#1
> >                 [33280 - 65535 pfns] - normal memory
> >
> >                 [memblock#2 ]
> >                 [65536 - 66047 pfns] - vmemmap for section#2
> >                 [66048 - 98304 pfns] - normal memory
> >
> > MHP_MEMMAP_DEVICE:
> >         - With this flag, we will store all vmemmap pages at the 
> > beginning of
> >           hot-added memory.
> >
> >           E.g:
> >                 We allocate a range (x,y], that spans 3 memory blocks, 
> > and given
> >                 memory block size = 128MB.
> >                 [memblock #0 ]
> >                 [0 - 1533 pfns    ] - vmemmap for section#{0-2}
> >                 [1534 - 98304 pfns] - normal memory
> >
> > When using larger memory blocks (1GB or 2GB), the principle is the 
> > same.
> >
> > Of course, MHP_MEMMAP_DEVICE is nicer when it comes to have a large 
> > contigous
> > area, while MHP_MEMMAP_MEMBLOCK allows us to have flexibility when 
> > removing the
> > memory.
>
> Concept and patch looks good to me, but I don't quite like the
> proliferation of the _DEVICE naming, in theory it need not necessarily
> be ZONE_DEVICE that is the only user of that flag. I also think it
> might be useful to assign a flag for the default 'allocate from RAM'
> case, just so the code is explicit. So, how about:
>
> MHP_MEMMAP_PAGE_ALLOC
> MHP_MEMMAP_MEMBLOCK
> MHP_MEMMAP_RESERVED
>
> ...for the 3 cases?
>
> Other than that, feel free to add:
>
> Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
 HI Dan,

I'll be sending V3 tomorrow, with some major rewrites (more simplified).

Thanks