On Wed, Oct 16, 2024 at 03:24:43PM -0400, Gregory Price wrote: > Hotplug memory sources may have opinions on what the memblock size > should be - usually for alignment purposes. For example, CXL memory > extents can be as small as 256MB with a matching physical alignment. > > Implement memblock_advise_size_order for use during early init, prior > to allocator and smp init, for software to advise the system as to what > the preferred block size should be. > > The probe function is meant for arch_init code to fetch this value > once during memblock size calculation. Use of the advisement value > is arch-specific, and no guarantee is made that it will be used. I'm confused. Aren't we talking about memory blocks for hotplugable memory here? This functionality rather belongs to drivers/base/memory.c, doesn't it? > Calls to either function after probe results in -EBUSY to signal that > advisement is ignored or that memblock_get_size_bytes should be used. > > Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx> > Signed-off-by: Gregory Price <gourry@xxxxxxxxxx> > --- > include/linux/memblock.h | 2 ++ > mm/memblock.c | 49 ++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 51 insertions(+) > > diff --git a/include/linux/memblock.h b/include/linux/memblock.h > index fc4d75c6cec3..efb1f7cfbd58 100644 > --- a/include/linux/memblock.h > +++ b/include/linux/memblock.h > @@ -111,6 +111,8 @@ static inline void memblock_discard(void) {} > #endif > > void memblock_allow_resize(void); > +int memblock_advise_size_order(int order); > +int memblock_probe_size_order(void); > int memblock_add_node(phys_addr_t base, phys_addr_t size, int nid, > enum memblock_flags flags); > int memblock_add(phys_addr_t base, phys_addr_t size); > diff --git a/mm/memblock.c b/mm/memblock.c > index 3b9dc2d89b8a..e0bdba011564 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -2009,6 +2009,55 @@ void __init memblock_allow_resize(void) > memblock_can_resize = 1; > } > > +/* > + * @order: bit-order describing the preferred minimum block size > + * > + * Intended for use by early-boot software prior to smp and allocator init to > + * advise the architecture what the minimum block size should be. Should only > + * be called during arch init before allocator and smp init. > + * > + * This value can only decrease after it has been initially set, the intention > + * is to identify the smallest supported alignment across all opinions. > + * > + * Use of this advisement value is arch-specific. > + * > + * Returns: 0 on success, -EINVAL if order is <=0, and -EBUSY if already probed > + */ > +static int memblock_sz_order; > +#define MEMBLOCK_SZO_PROBED (-1) > +int memblock_advise_size_order(int order) > +{ > + if (order <= 0) > + return -EINVAL; > + > + if (memblock_sz_order == MEMBLOCK_SZO_PROBED) > + return -EBUSY; > + > + if (memblock_sz_order) > + memblock_sz_order = min(order, memblock_sz_order); > + else > + memblock_sz_order = order; > + > + return 0; > +} > + > +/* > + * memblock_probe_size_order is intended for arch init code to probe one time, > + * for a suggested memory block size. After the first call, the result will > + * always be -EBUSY. A late user should call memory_block_size_bytes instead to > + * determine the actual block size in use. > + * > + * Should only be called during arch init prior to allocator and smp init. > + * > + * Returns: block size order, 0 if never set, or -EBUSY if previously probed. > + */ > +int memblock_probe_size_order(void) > +{ > + int rv = xchg(&memblock_sz_order, -1); > + > + return (rv == -1) ? -EBUSY : rv; > +} > + > static int __init early_memblock(char *p) > { > if (p && strstr(p, "debug")) > -- > 2.43.0 > -- Sincerely yours, Mike.