On 4/10/2023 10:47 AM, Joao Martins wrote:
On 10/04/2023 18:27, Jane Chu wrote:
On 4/8/2023 3:19 AM, Aneesh Kumar K.V wrote:
Jane Chu <jane.chu@xxxxxxxxxx> writes:
On 4/7/2023 5:23 AM, Aneesh Kumar K.V wrote:
diff --git a/mm/Kconfig b/mm/Kconfig
index ff7b209dec05..99f87c1be1e8 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -461,6 +461,9 @@ config SPARSEMEM_VMEMMAP
pfn_to_page and page_to_pfn operations. This is the most
efficient option when sufficient kernel resources are available.
+config ARCH_WANT_OPTIMIZE_VMEMMAP
+ bool
+
Could this devdax specific config switch be added to drivers/dax/Kconfig
? also, how about adding 'DAX' to the config switch name?
I would say we want to make it more generic. ie, both hugetlb and devdax
can now derive the feature support via ARCH_WANT_OPTIMIZE_VMEMAP
The two config switches have different purposes, it's better to keep them
separate. For example, recent hugetlb high granularity mapping (HGM) project
requires to users to make a choice between HGM and hugetlb vmemmap
optimization(at least for now), while one can keep devdax compound page support
enabled.
Is it done by kconfig? If it helps:
* there's a static key hugetlb can use to tell if this is enabled or not like
how page_fixed_fake_head() uses it:
if (!static_branch_unlikely(&hugetlb_optimize_vmemmap_key))
...
* there's a hugetlb page bit for that vmemmap optimized pages with
HpageOptimized(page).
* there is a separate hugetlb CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP which is not
the same as the ARCH kconfig.
But perhaps there's some relevance in the ARCH_HUGETLB specific to HGMv2 that I
am unaware.
Looks like there is no consumer of
CONFIG_ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP.
There are three ways to enable HVO via
CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON alone, or a combination
of CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP and boot param
'vmemmap_optimize_enabled' or sysctl variable
/proc/sys/vm/hugetlb_optimize_vmemmap.
It seems that the devdax compound page support does not cross path with
HVO which has a lot more moving arms, and so it's better to keep the
devdax config switch local to devdax and leave HVO alone.
thanks!
-jane
