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Message-ID: <ZyJKUAcn8iLoV7PI@PC2K9PVX.TheFacebook.com>
Date: Wed, 30 Oct 2024 11:01:36 -0400
From: Gregory Price <gourry@...rry.net>
To: David Hildenbrand <david@...hat.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
linux-acpi@...r.kernel.org, linux-mm@...ck.org,
linux-cxl@...r.kernel.org, Jonathan.Cameron@...wei.com,
dan.j.williams@...el.com, rrichter@....com, Terry.Bowman@....com,
dave.jiang@...el.com, ira.weiny@...el.com,
alison.schofield@...el.com, dave.hansen@...ux.intel.com,
luto@...nel.org, peterz@...radead.org, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, hpa@...or.com, rafael@...nel.org,
lenb@...nel.org, osalvador@...e.de, gregkh@...uxfoundation.org,
akpm@...ux-foundation.org, rppt@...nel.org
Subject: Re: [PATCH v4 3/3] acpi,srat: give memory block size advice based on
CFMWS alignment
On Wed, Oct 30, 2024 at 11:40:08AM +0100, David Hildenbrand wrote:
> On 29.10.24 21:20, Gregory Price wrote:
> > Capacity is stranded when CFMWS regions are not aligned to block size.
> > On x86, block size increases with capacity (2G blocks @ 64G capacity).
> >
> > Use CFMWS base/size to report memory block size alignment advice.
> >
> > Suggested-by: Dan Williams <dan.j.williams@...el.com>
> > Signed-off-by: Gregory Price <gourry@...rry.net>
> > ---
> > drivers/acpi/numa/srat.c | 19 +++++++++++++++++--
> > 1 file changed, 17 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/acpi/numa/srat.c b/drivers/acpi/numa/srat.c
> > index 44f91f2c6c5d..a24aff38c465 100644
> > --- a/drivers/acpi/numa/srat.c
> > +++ b/drivers/acpi/numa/srat.c
> > @@ -14,6 +14,7 @@
> > #include <linux/errno.h>
> > #include <linux/acpi.h>
> > #include <linux/memblock.h>
> > +#include <linux/memory.h>
> > #include <linux/numa.h>
> > #include <linux/nodemask.h>
> > #include <linux/topology.h>
> > @@ -338,12 +339,26 @@ static int __init acpi_parse_cfmws(union acpi_subtable_headers *header,
> > {
> > struct acpi_cedt_cfmws *cfmws;
> > int *fake_pxm = arg;
> > - u64 start, end;
> > + u64 start, end, align, size;
> > int node;
> > cfmws = (struct acpi_cedt_cfmws *)header;
> > start = cfmws->base_hpa;
> > - end = cfmws->base_hpa + cfmws->window_size;
> > + size = cfmws->window_size;
> > + end = cfmws->base_hpa + size;
> > +
> > + /* Align memblock size to CFMW regions if possible */
> > + for (align = SZ_64T; align >= SZ_256M; align >>= 1) {
> > + if (IS_ALIGNED(start, align) && IS_ALIGNED(size, align))
> > + break;
> > + }
>
> Are there maybe some nice tricks bi-tricks to avoid the loop and these
> hardcoded limits? :)
>
> align = 1UL << __ffs(start | end));
>
> Assuming "unsigned long" is sufficient in this code (64bit) and "start |
> end" will never be 0.
>
I don't think 0 itself is necessarily invalid, but it would be strange.
I can look a bit.
> --
> Cheers,
>
> David / dhildenb
>
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