Re: [PATCH V4 1/3] mm/sparsemem: Enable vmem_altmap support in vmemmap_populate_basepages()
From: David Hildenbrand <hidden>
Date: 2020-07-06 09:04:12
Also in:
linux-mm, linux-riscv, lkml
quoted hunk ↗ jump to hunk
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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel