The patch titled
Subject: mm: abstract THP allocation
has been added to the -mm mm-unstable branch. Its filename is
mm-abstract-thp-allocation.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-abstract-thp-allocation.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: Dev Jain <dev.jain@xxxxxxx>
Subject: mm: abstract THP allocation
Date: Tue, 8 Oct 2024 11:47:45 +0530
Patch series "Do not shatter hugezeropage on wp-fault", v7.
It was observed at [1] and [2] that the current kernel behaviour of
shattering a hugezeropage is inconsistent and suboptimal. For a VMA with
a THP allowable order, when we write-fault on it, the kernel installs a
PMD-mapped THP. On the other hand, if we first get a read fault, we get a
PMD pointing to the hugezeropage; subsequent write will trigger a
write-protection fault, shattering the hugezeropage into one writable
page, and all the other PTEs write-protected. The conclusion being, as
compared to the case of a single write-fault, applications have to suffer
512 extra page faults if they were to use the VMA as such, plus we get the
overhead of khugepaged trying to replace that area with a THP anyway.
Instead, replace the hugezeropage with a THP on wp-fault.
[1]: https://lore.kernel.org/all/3743d7e1-0b79-4eaf-82d5-d1ca29fe347d@xxxxxxx/
[2]: https://lore.kernel.org/all/1cfae0c0-96a2-4308-9c62-f7a640520242@xxxxxxx/
This patch (of 2):
In preparation for the second patch, abstract away the THP allocation
logic present in the create_huge_pmd() path, which corresponds to the
faulting case when no page is present.
There should be no functional change as a result of applying this patch,
except that, as David notes at [1], a PMD-aligned address should be passed
to update_mmu_cache_pmd().
[1]: https://lore.kernel.org/all/ddd3fcd2-48b3-4170-bcaa-2fe66e093f43@xxxxxxxxxx/
Link: https://lkml.kernel.org/r/20241008061746.285961-1-dev.jain@xxxxxxx
Link: https://lkml.kernel.org/r/20241008061746.285961-2-dev.jain@xxxxxxx
Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: Barry Song <baohua@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Lance Yang <ioworker0@xxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 98 ++++++++++++++++++++++++++-------------------
1 file changed, 57 insertions(+), 41 deletions(-)
--- a/mm/huge_memory.c~mm-abstract-thp-allocation
+++ a/mm/huge_memory.c
@@ -1150,47 +1150,81 @@ unsigned long thp_get_unmapped_area(stru
}
EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
-static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
- struct page *page, gfp_t gfp)
+static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
+ unsigned long addr)
{
- struct vm_area_struct *vma = vmf->vma;
- struct folio *folio = page_folio(page);
- pgtable_t pgtable;
- unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
- vm_fault_t ret = 0;
+ gfp_t gfp = vma_thp_gfp_mask(vma);
+ const int order = HPAGE_PMD_ORDER;
+ struct folio *folio;
- VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
+ folio = vma_alloc_folio(gfp, order, vma, addr & HPAGE_PMD_MASK, true);
+ if (unlikely(!folio)) {
+ count_vm_event(THP_FAULT_FALLBACK);
+ count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
+ return NULL;
+ }
+
+ VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
folio_put(folio);
count_vm_event(THP_FAULT_FALLBACK);
count_vm_event(THP_FAULT_FALLBACK_CHARGE);
- count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK);
- count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
- return VM_FAULT_FALLBACK;
+ count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
+ count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
+ return NULL;
}
folio_throttle_swaprate(folio, gfp);
- pgtable = pte_alloc_one(vma->vm_mm);
- if (unlikely(!pgtable)) {
- ret = VM_FAULT_OOM;
- goto release;
- }
-
- folio_zero_user(folio, vmf->address);
+ folio_zero_user(folio, addr);
/*
* The memory barrier inside __folio_mark_uptodate makes sure that
* folio_zero_user writes become visible before the set_pmd_at()
* write.
*/
__folio_mark_uptodate(folio);
+ return folio;
+}
+
+static void map_anon_folio_pmd(struct folio *folio, pmd_t *pmd,
+ struct vm_area_struct *vma, unsigned long haddr)
+{
+ pmd_t entry;
+
+ entry = mk_huge_pmd(&folio->page, vma->vm_page_prot);
+ entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+ folio_add_new_anon_rmap(folio, vma, haddr, RMAP_EXCLUSIVE);
+ folio_add_lru_vma(folio, vma);
+ set_pmd_at(vma->vm_mm, haddr, pmd, entry);
+ update_mmu_cache_pmd(vma, haddr, pmd);
+ add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
+ count_vm_event(THP_FAULT_ALLOC);
+ count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_ALLOC);
+ count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
+}
+
+static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
+{
+ unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
+ struct vm_area_struct *vma = vmf->vma;
+ struct folio *folio;
+ pgtable_t pgtable;
+ vm_fault_t ret = 0;
+
+ folio = vma_alloc_anon_folio_pmd(vma, vmf->address);
+ if (unlikely(!folio))
+ return VM_FAULT_FALLBACK;
+
+ pgtable = pte_alloc_one(vma->vm_mm);
+ if (unlikely(!pgtable)) {
+ ret = VM_FAULT_OOM;
+ goto release;
+ }
vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
if (unlikely(!pmd_none(*vmf->pmd))) {
goto unlock_release;
} else {
- pmd_t entry;
-
ret = check_stable_address_space(vma->vm_mm);
if (ret)
goto unlock_release;
@@ -1204,21 +1238,11 @@ static vm_fault_t __do_huge_pmd_anonymou
VM_BUG_ON(ret & VM_FAULT_FALLBACK);
return ret;
}
-
- entry = mk_huge_pmd(page, vma->vm_page_prot);
- entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
- folio_add_new_anon_rmap(folio, vma, haddr, RMAP_EXCLUSIVE);
- folio_add_lru_vma(folio, vma);
pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
- set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
- update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
- add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
+ map_anon_folio_pmd(folio, vmf->pmd, vma, haddr);
mm_inc_nr_ptes(vma->vm_mm);
deferred_split_folio(folio, false);
spin_unlock(vmf->ptl);
- count_vm_event(THP_FAULT_ALLOC);
- count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_ALLOC);
- count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
}
return 0;
@@ -1285,8 +1309,6 @@ static void set_huge_zero_folio(pgtable_
vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
- gfp_t gfp;
- struct folio *folio;
unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
vm_fault_t ret;
@@ -1337,14 +1359,8 @@ vm_fault_t do_huge_pmd_anonymous_page(st
}
return ret;
}
- gfp = vma_thp_gfp_mask(vma);
- folio = vma_alloc_folio(gfp, HPAGE_PMD_ORDER, vma, haddr, true);
- if (unlikely(!folio)) {
- count_vm_event(THP_FAULT_FALLBACK);
- count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK);
- return VM_FAULT_FALLBACK;
- }
- return __do_huge_pmd_anonymous_page(vmf, &folio->page, gfp);
+
+ return __do_huge_pmd_anonymous_page(vmf);
}
static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
_
Patches currently in -mm which might be from dev.jain@xxxxxxx are
mm-abstract-thp-allocation.patch
mm-allocate-thp-on-hugezeropage-wp-fault.patch
