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Message-ID: <e3d13396-8408-49c0-9ec9-1b02790959aa@redhat.com>
Date: Wed, 6 Aug 2025 12:11:33 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, ryan.roberts@....com, willy@...radead.org,
linux-mm@...ck.org, linux-kernel@...r.kernel.org, catalin.marinas@....com,
will@...nel.org, Liam.Howlett@...cle.com, vbabka@...e.cz, jannh@...gle.com,
anshuman.khandual@....com, peterx@...hat.com, joey.gouly@....com,
ioworker0@...il.com, baohua@...nel.org, kevin.brodsky@....com,
quic_zhenhuah@...cinc.com, christophe.leroy@...roup.eu,
yangyicong@...ilicon.com, linux-arm-kernel@...ts.infradead.org,
hughd@...gle.com, yang@...amperecomputing.com, ziy@...dia.com
Subject: Re: [PATCH v5 6/7] mm: Optimize mprotect() by PTE batching
On 06.08.25 11:50, Lorenzo Stoakes wrote:
> On Wed, Aug 06, 2025 at 03:07:49PM +0530, Dev Jain wrote:
>>>>
>>>> You mean in _this_ PTE of the batch right? As we're invoking these
>>>> on each part
>>>> of the PTE table.
>>>>
>>>> I mean I guess we can simply do:
>>>>
>>>> struct page *first_page = pte_page(ptent);
>>>>
>>>> Right?
>>>
>>> Yes, but we should forward the result from vm_normal_page(), which does
>>> exactly that for you, and increment the page accordingly as required,
>>> just like with the pte we are processing.
>>
>> Makes sense, so I guess I will have to change the signature of
>> prot_numa_skip()
>>
>> to pass a double ptr to a page instead of folio and derive the folio in the
>> caller,
>>
>> and pass down both the folio and the page to
>> set_write_prot_commit_flush_ptes.
>
> I already don't love how we psas the folio back from there for very dubious
> benefit. I really hate the idea of having a struct **page parameter...
>
> I wonder if we should just have a quick fixup for hotfix, and refine this more
> later?
This is not an issue in any released kernel, so we can do this properly.
We should just remove that nested vm_normal_folio().
Untested, but should give an idea what we can do.
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 78bded7acf795..4e0a22f7db495 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -120,7 +120,7 @@ static int mprotect_folio_pte_batch(struct folio *folio, pte_t *ptep,
static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr,
pte_t oldpte, pte_t *pte, int target_node,
- struct folio **foliop)
+ struct folio *folio)
{
struct folio *folio = NULL;
bool ret = true;
@@ -131,7 +131,6 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr,
if (pte_protnone(oldpte))
goto skip;
- folio = vm_normal_folio(vma, addr, oldpte);
if (!folio)
goto skip;
@@ -172,8 +171,6 @@ static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr,
if (folio_use_access_time(folio))
folio_xchg_access_time(folio, jiffies_to_msecs(jiffies));
-skip:
- *foliop = folio;
return ret;
}
@@ -231,10 +228,9 @@ static int page_anon_exclusive_sub_batch(int start_idx, int max_len,
* retrieve sub-batches.
*/
static void commit_anon_folio_batch(struct vm_area_struct *vma,
- struct folio *folio, unsigned long addr, pte_t *ptep,
+ struct folio *folio, struct page *first_page, unsigned long addr, pte_t *ptep,
pte_t oldpte, pte_t ptent, int nr_ptes, struct mmu_gather *tlb)
{
- struct page *first_page = folio_page(folio, 0);
bool expected_anon_exclusive;
int sub_batch_idx = 0;
int len;
@@ -243,7 +239,7 @@ static void commit_anon_folio_batch(struct vm_area_struct *vma,
expected_anon_exclusive = PageAnonExclusive(first_page + sub_batch_idx);
len = page_anon_exclusive_sub_batch(sub_batch_idx, nr_ptes,
first_page, expected_anon_exclusive);
- prot_commit_flush_ptes(vma, addr, ptep, oldpte, ptent, len,
+ prot_commit_flush_ptes(vma, addr, ptep, page, oldpte, ptent, len,
sub_batch_idx, expected_anon_exclusive, tlb);
sub_batch_idx += len;
nr_ptes -= len;
@@ -251,7 +247,7 @@ static void commit_anon_folio_batch(struct vm_area_struct *vma,
}
static void set_write_prot_commit_flush_ptes(struct vm_area_struct *vma,
- struct folio *folio, unsigned long addr, pte_t *ptep,
+ struct folio *folio, struct page *page, unsigned long addr, pte_t *ptep,
pte_t oldpte, pte_t ptent, int nr_ptes, struct mmu_gather *tlb)
{
bool set_write;
@@ -270,7 +266,7 @@ static void set_write_prot_commit_flush_ptes(struct vm_area_struct *vma,
/* idx = */ 0, set_write, tlb);
return;
}
- commit_anon_folio_batch(vma, folio, addr, ptep, oldpte, ptent, nr_ptes, tlb);
+ commit_anon_folio_batch(vma, folio, page, addr, ptep, oldpte, ptent, nr_ptes, tlb);
}
static long change_pte_range(struct mmu_gather *tlb,
@@ -305,15 +301,20 @@ static long change_pte_range(struct mmu_gather *tlb,
const fpb_t flags = FPB_RESPECT_SOFT_DIRTY | FPB_RESPECT_WRITE;
int max_nr_ptes = (end - addr) >> PAGE_SHIFT;
struct folio *folio = NULL;
+ struct page *page;
pte_t ptent;
+ page = vm_normal_folio(vma, addr, oldpte);
+ if (page)
+ folio = page_folio(page);
+
/*
* Avoid trapping faults against the zero or KSM
* pages. See similar comment in change_huge_pmd.
*/
if (prot_numa) {
int ret = prot_numa_skip(vma, addr, oldpte, pte,
- target_node, &folio);
+ target_node, folio);
if (ret) {
/* determine batch to skip */
@@ -323,9 +324,6 @@ static long change_pte_range(struct mmu_gather *tlb,
}
}
- if (!folio)
- folio = vm_normal_folio(vma, addr, oldpte);
-
nr_ptes = mprotect_folio_pte_batch(folio, pte, oldpte, max_nr_ptes, flags);
oldpte = modify_prot_start_ptes(vma, addr, pte, nr_ptes);
@@ -351,7 +349,7 @@ static long change_pte_range(struct mmu_gather *tlb,
*/
if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) &&
!pte_write(ptent))
- set_write_prot_commit_flush_ptes(vma, folio,
+ set_write_prot_commit_flush_ptes(vma, folio, page,
addr, pte, oldpte, ptent, nr_ptes, tlb);
else
prot_commit_flush_ptes(vma, addr, pte, oldpte, ptent,
--
2.50.1
--
Cheers,
David / dhildenb
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