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Subject[PATCH 7/7] mm/gup: Cache dev_pagemap while pinning pages
Date
This avoids a repeated costly radix tree lookup when dev_pagemap is
used.

Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
---
include/linux/mm.h | 8 +++++++-
mm/gup.c | 41 ++++++++++++++++++++++++-----------------
mm/huge_memory.c | 35 +++++++++++++++--------------------
3 files changed, 46 insertions(+), 38 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f1fd241c9071..d688e18a19c4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -380,6 +380,7 @@ struct vm_fault {

struct follow_page_context {
struct vm_area_struct *vma;
+ struct dev_pagemap *pgmap;
unsigned long address;
unsigned int page_mask;
unsigned int flags;
@@ -2546,14 +2547,19 @@ struct page *follow_page_mask(struct follow_page_context *ctx);
static inline struct page *follow_page(struct vm_area_struct *vma,
unsigned long address, unsigned int foll_flags)
{
+ struct page *page;
struct follow_page_context ctx = {
.vma = vma,
+ .pgmap = NULL,
.address = address,
.page_mask = 0,
.flags = foll_flags,
};

- return follow_page_mask(&ctx);
+ page = follow_page_mask(&ctx);
+ if (ctx.pgmap)
+ put_dev_pagemap(ctx.pgmap);
+ return page;
}

#define FOLL_WRITE 0x01 /* check pte is writable */
diff --git a/mm/gup.c b/mm/gup.c
index a61a6874c80c..1565b79d883b 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -72,7 +72,6 @@ static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
static struct page *follow_page_pte(struct follow_page_context *ctx, pmd_t *pmd)
{
struct mm_struct *mm = ctx->vma->vm_mm;
- struct dev_pagemap *pgmap = NULL;
struct page *page;
spinlock_t *ptl;
pte_t *ptep, pte;
@@ -114,8 +113,8 @@ static struct page *follow_page_pte(struct follow_page_context *ctx, pmd_t *pmd)
* Only return device mapping pages in the FOLL_GET case since
* they are only valid while holding the pgmap reference.
*/
- pgmap = get_dev_pagemap(pte_pfn(pte), NULL);
- if (pgmap)
+ ctx->pgmap = get_dev_pagemap(pte_pfn(pte), ctx->pgmap);
+ if (ctx->pgmap)
page = pte_page(pte);
else
goto no_page;
@@ -154,9 +153,9 @@ static struct page *follow_page_pte(struct follow_page_context *ctx, pmd_t *pmd)
get_page(page);

/* drop the pgmap reference now that we hold the page */
- if (pgmap) {
- put_dev_pagemap(pgmap);
- pgmap = NULL;
+ if (ctx->pgmap) {
+ put_dev_pagemap(ctx->pgmap);
+ ctx->pgmap = NULL;
}
}
if (ctx->flags & FOLL_TOUCH) {
@@ -645,7 +644,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas, int *nonblocking)
{
- long i = 0;
+ long ret = 0, i = 0;
struct vm_area_struct *vma = NULL;
struct follow_page_context ctx = {};

@@ -681,8 +680,10 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
goto next_page;
}

- if (!vma || check_vma_flags(vma, gup_flags))
- return i ? : -EFAULT;
+ if (!vma || check_vma_flags(vma, gup_flags)) {
+ ret = -EFAULT;
+ goto out;
+ }
if (is_vm_hugetlb_page(vma)) {
i = follow_hugetlb_page(mm, vma, pages, vmas,
&start, &nr_pages, i,
@@ -697,23 +698,25 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
* If we have a pending SIGKILL, don't keep faulting pages and
* potentially allocating memory.
*/
- if (unlikely(fatal_signal_pending(current)))
- return i ? i : -ERESTARTSYS;
+ if (unlikely(fatal_signal_pending(current))) {
+ ret = -ERESTARTSYS;
+ goto out;
+ }
cond_resched();

page = follow_page_mask(&ctx);
if (!page) {
- int ret;
ret = faultin_page(tsk, &ctx, nonblocking);
switch (ret) {
case 0:
goto retry;
+ case -EBUSY:
+ ret = 0;
+ /* FALLTHRU */
case -EFAULT:
case -ENOMEM:
case -EHWPOISON:
- return i ? i : ret;
- case -EBUSY:
- return i;
+ goto out;
case -ENOENT:
goto next_page;
}
@@ -725,7 +728,8 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
*/
goto next_page;
} else if (IS_ERR(page)) {
- return i ? i : PTR_ERR(page);
+ ret = PTR_ERR(page);
+ goto out;
}
if (pages) {
pages[i] = page;
@@ -745,7 +749,10 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
start += page_increm * PAGE_SIZE;
nr_pages -= page_increm;
} while (nr_pages);
- return i;
+out:
+ if (ctx.pgmap)
+ put_dev_pagemap(ctx.pgmap);
+ return i ? i : ret;
}

static bool vma_permits_fault(struct vm_area_struct *vma,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index abd36e6afe2c..6787011385ce 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -851,12 +851,23 @@ static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
update_mmu_cache_pmd(vma, addr, pmd);
}

+static struct page *pagemap_page(struct follow_page_context *ctx,
+ unsigned long pfn)
+{
+ struct page *page;
+
+ ctx->pgmap = get_dev_pagemap(pfn, ctx->pgmap);
+ if (!ctx->pgmap)
+ return ERR_PTR(-EFAULT);
+ page = pfn_to_page(pfn);
+ get_page(page);
+ return page;
+}
+
struct page *follow_devmap_pmd(struct follow_page_context *ctx, pmd_t *pmd)
{
unsigned long pfn = pmd_pfn(*pmd);
struct mm_struct *mm = ctx->vma->vm_mm;
- struct dev_pagemap *pgmap;
- struct page *page;

assert_spin_locked(pmd_lockptr(mm, pmd));

@@ -885,14 +896,7 @@ struct page *follow_devmap_pmd(struct follow_page_context *ctx, pmd_t *pmd)
return ERR_PTR(-EEXIST);

pfn += (ctx->address & ~PMD_MASK) >> PAGE_SHIFT;
- pgmap = get_dev_pagemap(pfn, NULL);
- if (!pgmap)
- return ERR_PTR(-EFAULT);
- page = pfn_to_page(pfn);
- get_page(page);
- put_dev_pagemap(pgmap);
-
- return page;
+ return pagemap_page(ctx, pfn);
}

int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
@@ -1002,8 +1006,6 @@ struct page *follow_devmap_pud(struct follow_page_context *ctx, pud_t *pud)
{
unsigned long pfn = pud_pfn(*pud);
struct mm_struct *mm = ctx->vma->vm_mm;
- struct dev_pagemap *pgmap;
- struct page *page;

assert_spin_locked(pud_lockptr(mm, pud));

@@ -1026,14 +1028,7 @@ struct page *follow_devmap_pud(struct follow_page_context *ctx, pud_t *pud)
return ERR_PTR(-EEXIST);

pfn += (ctx->address & ~PUD_MASK) >> PAGE_SHIFT;
- pgmap = get_dev_pagemap(pfn, NULL);
- if (!pgmap)
- return ERR_PTR(-EFAULT);
- page = pfn_to_page(pfn);
- get_page(page);
- put_dev_pagemap(pgmap);
-
- return page;
+ return pagemap_page(ctx, pfn);
}

int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
--
2.14.4
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