The patch titled
Subject: hugetlb: batch PMD split for bulk vmemmap dedup
has been added to the -mm mm-unstable branch. Its filename is
hugetlb-batch-pmd-split-for-bulk-vmemmap-dedup.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/hugetlb-batch-pmd-split-for-bulk-vmemmap-dedup.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Joao Martins <joao.m.martins@xxxxxxxxxx>
Subject: hugetlb: batch PMD split for bulk vmemmap dedup
Date: Thu, 5 Oct 2023 20:20:08 -0700
In an effort to minimize amount of TLB flushes, batch all PMD splits
belonging to a range of pages in order to perform only 1 (global) TLB
flush.
Add a flags field to the walker and pass whether it's a bulk allocation or
just a single page to decide to remap. First value
(VMEMMAP_SPLIT_NO_TLB_FLUSH) designates the request to not do the TLB
flush when we split the PMD.
Rebased and updated by Mike Kravetz
Link: https://lkml.kernel.org/r/20231006032012.296473-7-mike.kravetz@xxxxxxxxxx
Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: Barry Song <21cnbao@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: James Houghton <jthoughton@xxxxxxxxxx>
Cc: Konrad Dybcio <konradybcio@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Xiongchun Duan <duanxiongchun@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb_vmemmap.c | 92 +++++++++++++++++++++++++++++++++++++++--
1 file changed, 88 insertions(+), 4 deletions(-)
--- a/mm/hugetlb_vmemmap.c~hugetlb-batch-pmd-split-for-bulk-vmemmap-dedup
+++ a/mm/hugetlb_vmemmap.c
@@ -27,6 +27,8 @@
* @reuse_addr: the virtual address of the @reuse_page page.
* @vmemmap_pages: the list head of the vmemmap pages that can be freed
* or is mapped from.
+ * @flags: used to modify behavior in vmemmap page table walking
+ * operations.
*/
struct vmemmap_remap_walk {
void (*remap_pte)(pte_t *pte, unsigned long addr,
@@ -35,9 +37,13 @@ struct vmemmap_remap_walk {
struct page *reuse_page;
unsigned long reuse_addr;
struct list_head *vmemmap_pages;
+
+/* Skip the TLB flush when we split the PMD */
+#define VMEMMAP_SPLIT_NO_TLB_FLUSH BIT(0)
+ unsigned long flags;
};
-static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
+static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start, bool flush)
{
pmd_t __pmd;
int i;
@@ -80,7 +86,8 @@ static int split_vmemmap_huge_pmd(pmd_t
/* Make pte visible before pmd. See comment in pmd_install(). */
smp_wmb();
pmd_populate_kernel(&init_mm, pmd, pgtable);
- flush_tlb_kernel_range(start, start + PMD_SIZE);
+ if (flush)
+ flush_tlb_kernel_range(start, start + PMD_SIZE);
} else {
pte_free_kernel(&init_mm, pgtable);
}
@@ -127,11 +134,20 @@ static int vmemmap_pmd_range(pud_t *pud,
do {
int ret;
- ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK);
+ ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK,
+ !(walk->flags & VMEMMAP_SPLIT_NO_TLB_FLUSH));
if (ret)
return ret;
next = pmd_addr_end(addr, end);
+
+ /*
+ * We are only splitting, not remapping the hugetlb vmemmap
+ * pages.
+ */
+ if (!walk->remap_pte)
+ continue;
+
vmemmap_pte_range(pmd, addr, next, walk);
} while (pmd++, addr = next, addr != end);
@@ -198,7 +214,8 @@ static int vmemmap_remap_range(unsigned
return ret;
} while (pgd++, addr = next, addr != end);
- flush_tlb_kernel_range(start, end);
+ if (walk->remap_pte)
+ flush_tlb_kernel_range(start, end);
return 0;
}
@@ -298,6 +315,36 @@ static void vmemmap_restore_pte(pte_t *p
}
/**
+ * vmemmap_remap_split - split the vmemmap virtual address range [@start, @end)
+ * backing PMDs of the directmap into PTEs
+ * @start: start address of the vmemmap virtual address range that we want
+ * to remap.
+ * @end: end address of the vmemmap virtual address range that we want to
+ * remap.
+ * @reuse: reuse address.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+static int vmemmap_remap_split(unsigned long start, unsigned long end,
+ unsigned long reuse)
+{
+ int ret;
+ struct vmemmap_remap_walk walk = {
+ .remap_pte = NULL,
+ .flags = VMEMMAP_SPLIT_NO_TLB_FLUSH,
+ };
+
+ /* See the comment in the vmemmap_remap_free(). */
+ BUG_ON(start - reuse != PAGE_SIZE);
+
+ mmap_read_lock(&init_mm);
+ ret = vmemmap_remap_range(reuse, end, &walk);
+ mmap_read_unlock(&init_mm);
+
+ return ret;
+}
+
+/**
* vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
* to the page which @reuse is mapped to, then free vmemmap
* which the range are mapped to.
@@ -320,6 +367,7 @@ static int vmemmap_remap_free(unsigned l
.remap_pte = vmemmap_remap_pte,
.reuse_addr = reuse,
.vmemmap_pages = vmemmap_pages,
+ .flags = 0,
};
int nid = page_to_nid((struct page *)reuse);
gfp_t gfp_mask = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
@@ -368,6 +416,7 @@ static int vmemmap_remap_free(unsigned l
.remap_pte = vmemmap_restore_pte,
.reuse_addr = reuse,
.vmemmap_pages = vmemmap_pages,
+ .flags = 0,
};
vmemmap_remap_range(reuse, end, &walk);
@@ -419,6 +468,7 @@ static int vmemmap_remap_alloc(unsigned
.remap_pte = vmemmap_restore_pte,
.reuse_addr = reuse,
.vmemmap_pages = &vmemmap_pages,
+ .flags = 0,
};
/* See the comment in the vmemmap_remap_free(). */
@@ -628,12 +678,46 @@ void hugetlb_vmemmap_optimize(const stru
free_vmemmap_page_list(&vmemmap_pages);
}
+static int hugetlb_vmemmap_split(const struct hstate *h, struct page *head)
+{
+ unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
+ unsigned long vmemmap_reuse;
+
+ if (!vmemmap_should_optimize(h, head))
+ return 0;
+
+ vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
+ vmemmap_reuse = vmemmap_start;
+ vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
+
+ /*
+ * Split PMDs on the vmemmap virtual address range [@vmemmap_start,
+ * @vmemmap_end]
+ */
+ return vmemmap_remap_split(vmemmap_start, vmemmap_end, vmemmap_reuse);
+}
+
void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list)
{
struct folio *folio;
LIST_HEAD(vmemmap_pages);
list_for_each_entry(folio, folio_list, lru) {
+ int ret = hugetlb_vmemmap_split(h, &folio->page);
+
+ /*
+ * Spliting the PMD requires allocating a page, thus lets fail
+ * early once we encounter the first OOM. No point in retrying
+ * as it can be dynamically done on remap with the memory
+ * we get back from the vmemmap deduplication.
+ */
+ if (ret == -ENOMEM)
+ break;
+ }
+
+ flush_tlb_all();
+
+ list_for_each_entry(folio, folio_list, lru) {
int ret = __hugetlb_vmemmap_optimize(h, &folio->page,
&vmemmap_pages);
_
Patches currently in -mm which might be from joao.m.martins@xxxxxxxxxx are
hugetlb-batch-pmd-split-for-bulk-vmemmap-dedup.patch
hugetlb-batch-tlb-flushes-when-freeing-vmemmap.patch
