Messages in this thread | | | Subject | Re: [PATCH V4 1/3] mm/sparsemem: Enable vmem_altmap support in vmemmap_populate_basepages() | From | David Hildenbrand <> | Date | Mon, 6 Jul 2020 11:03:47 +0200 |
| |
> return 0; > @@ -1505,7 +1505,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, > int err; > > if (end - start < PAGES_PER_SECTION * sizeof(struct page)) > - err = vmemmap_populate_basepages(start, end, node); > + err = vmemmap_populate_basepages(start, end, node, NULL); > else if (boot_cpu_has(X86_FEATURE_PSE)) > err = vmemmap_populate_hugepages(start, end, node, altmap); > else if (altmap) {
It's somewhat weird that we don't allocate basepages from altmap on x86 (both for sub-sections and without PSE). I wonder if we can simply unlock that with your change. Especially, also handle the !X86_FEATURE_PSE case below properly with an altmap.
a) all hw with PMEM has PSE - except special QEMU setups, so nobody cared to implement. For the sub-section special case, nobody cared about a handfull of memmap not ending up on the altmap. (but it's still wasted system memory IIRC).
b) the pagetable overhead for small pages is not-neglectable and might result in similar issues as solved by the switch to altmap on very huge PMEM (with small amount of system RAM).
I guess it is due to a).
[...]
> > -pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node) > +pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node, > + struct vmem_altmap *altmap) > { > pte_t *pte = pte_offset_kernel(pmd, addr); > if (pte_none(*pte)) { > pte_t entry; > - void *p = vmemmap_alloc_block_buf(PAGE_SIZE, node); > + void *p; > + > + if (altmap) > + p = altmap_alloc_block_buf(PAGE_SIZE, altmap); > + else > + p = vmemmap_alloc_block_buf(PAGE_SIZE, node); > if (!p) > return NULL;
I was wondering if
if (altmap) p = altmap_alloc_block_buf(PAGE_SIZE, altmap); if (!p) p = vmemmap_alloc_block_buf(PAGE_SIZE, node); if (!p) return NULL
Would make sense. But I guess this isn't really relevant in practice, because the altmap is usually sized properly.
In general, LGTM.
-- Thanks,
David / dhildenb
| |