[PATCHv3 6/6] mm/gup: Cache dev_pagemap while pinning pages

From: Keith Busch
Date: Fri Sep 21 2018 - 18:44:12 EST

Pinning pages from ZONE_DEVICE memory needs to check the backing device's
live-ness, which is tracked in the device's dev_pagemap metadata. This
metadata is stored in a radix tree and looking it up adds measurable
software overhead.

This patch avoids repeating this relatively costly operation when
dev_pagemap is used by caching the last dev_pagemap when getting user
pages. The gup_benchmark reports this reduces the time to get user pages
to as low as 1/3 of the previous time.

The cached value is combined with other output parameters into a context
struct to keep the parameters fewer.

Cc: Kirill Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Keith Busch <keith.busch@xxxxxxxxx>
---
include/linux/huge_mm.h | 8 ++---
include/linux/mm.h | 19 +++++++++--
mm/gup.c | 90 +++++++++++++++++++++++++++----------------------
mm/huge_memory.c | 38 +++++++++------------
mm/nommu.c | 4 +--
5 files changed, 88 insertions(+), 71 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 99c19b06d9a4..5cbabdebe9af 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -213,9 +213,9 @@ static inline int hpage_nr_pages(struct page *page)
}

struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
- pmd_t *pmd, int flags);
+ pmd_t *pmd, int flags, struct dev_pagemap **pgmap);
struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
- pud_t *pud, int flags);
+ pud_t *pud, int flags, struct dev_pagemap **pgmap);

extern vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t orig_pmd);

@@ -344,13 +344,13 @@ static inline void mm_put_huge_zero_page(struct mm_struct *mm)
}

static inline struct page *follow_devmap_pmd(struct vm_area_struct *vma,
- unsigned long addr, pmd_t *pmd, int flags)
+ unsigned long addr, pmd_t *pmd, int flags, struct dev_pagemap **pgmap)
{
return NULL;
}

static inline struct page *follow_devmap_pud(struct vm_area_struct *vma,
- unsigned long addr, pud_t *pud, int flags)
+ unsigned long addr, pud_t *pud, int flags, struct dev_pagemap **pgmap)
{
return NULL;
}
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a61ebe8ad4ca..79c80496dd50 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2534,15 +2534,28 @@ static inline vm_fault_t vmf_error(int err)
return VM_FAULT_SIGBUS;
}

+struct follow_page_context {
+ struct dev_pagemap *pgmap;
+ unsigned int page_mask;
+};
+
struct page *follow_page_mask(struct vm_area_struct *vma,
unsigned long address, unsigned int foll_flags,
- unsigned int *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)
{
- unsigned int unused_page_mask;
- return follow_page_mask(vma, address, foll_flags, &unused_page_mask);
+ struct page *page;
+ struct follow_page_context ctx = {
+ .pgmap = NULL,
+ .page_mask = 0,
+ };
+
+ page = follow_page_mask(vma, address, foll_flags, &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 1abc8b4afff6..124e7293e381 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -71,10 +71,10 @@ static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
}

static struct page *follow_page_pte(struct vm_area_struct *vma,
- unsigned long address, pmd_t *pmd, unsigned int flags)
+ unsigned long address, pmd_t *pmd, unsigned int flags,
+ struct dev_pagemap **pgmap)
{
struct mm_struct *mm = vma->vm_mm;
- struct dev_pagemap *pgmap = NULL;
struct page *page;
spinlock_t *ptl;
pte_t *ptep, pte;
@@ -116,8 +116,8 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
* 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)
+ *pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap);
+ if (*pgmap)
page = pte_page(pte);
else
goto no_page;
@@ -156,9 +156,9 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
get_page(page);

/* drop the pgmap reference now that we hold the page */
- if (pgmap) {
- put_dev_pagemap(pgmap);
- pgmap = NULL;
+ if (*pgmap) {
+ put_dev_pagemap(*pgmap);
+ *pgmap = NULL;
}
}
if (flags & FOLL_TOUCH) {
@@ -210,7 +210,8 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,

static struct page *follow_pmd_mask(struct vm_area_struct *vma,
unsigned long address, pud_t *pudp,
- unsigned int flags, unsigned int *page_mask)
+ unsigned int flags,
+ struct follow_page_context *ctx)
{
pmd_t *pmd, pmdval;
spinlock_t *ptl;
@@ -258,13 +259,13 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
}
if (pmd_devmap(pmdval)) {
ptl = pmd_lock(mm, pmd);
- page = follow_devmap_pmd(vma, address, pmd, flags);
+ page = follow_devmap_pmd(vma, address, pmd, flags, &ctx->pgmap);
spin_unlock(ptl);
if (page)
return page;
}
if (likely(!pmd_trans_huge(pmdval)))
- return follow_page_pte(vma, address, pmd, flags);
+ return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);

if ((flags & FOLL_NUMA) && pmd_protnone(pmdval))
return no_page_table(vma, flags);
@@ -284,7 +285,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
}
if (unlikely(!pmd_trans_huge(*pmd))) {
spin_unlock(ptl);
- return follow_page_pte(vma, address, pmd, flags);
+ return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
}
if (flags & FOLL_SPLIT) {
int ret;
@@ -307,18 +308,18 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
}

return ret ? ERR_PTR(ret) :
- follow_page_pte(vma, address, pmd, flags);
+ follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
}
page = follow_trans_huge_pmd(vma, address, pmd, flags);
spin_unlock(ptl);
- *page_mask = HPAGE_PMD_NR - 1;
+ ctx->page_mask = HPAGE_PMD_NR - 1;
return page;
}

-
static struct page *follow_pud_mask(struct vm_area_struct *vma,
unsigned long address, p4d_t *p4dp,
- unsigned int flags, unsigned int *page_mask)
+ unsigned int flags,
+ struct follow_page_context *ctx)
{
pud_t *pud;
spinlock_t *ptl;
@@ -344,7 +345,7 @@ static struct page *follow_pud_mask(struct vm_area_struct *vma,
}
if (pud_devmap(*pud)) {
ptl = pud_lock(mm, pud);
- page = follow_devmap_pud(vma, address, pud, flags);
+ page = follow_devmap_pud(vma, address, pud, flags, &ctx->pgmap);
spin_unlock(ptl);
if (page)
return page;
@@ -352,13 +353,13 @@ static struct page *follow_pud_mask(struct vm_area_struct *vma,
if (unlikely(pud_bad(*pud)))
return no_page_table(vma, flags);

- return follow_pmd_mask(vma, address, pud, flags, page_mask);
+ return follow_pmd_mask(vma, address, pud, flags, ctx);
}

-
static struct page *follow_p4d_mask(struct vm_area_struct *vma,
unsigned long address, pgd_t *pgdp,
- unsigned int flags, unsigned int *page_mask)
+ unsigned int flags,
+ struct follow_page_context *ctx)
{
p4d_t *p4d;
struct page *page;
@@ -378,7 +379,7 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma,
return page;
return no_page_table(vma, flags);
}
- return follow_pud_mask(vma, address, p4d, flags, page_mask);
+ return follow_pud_mask(vma, address, p4d, flags, ctx);
}

/**
@@ -396,13 +397,13 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma,
*/
struct page *follow_page_mask(struct vm_area_struct *vma,
unsigned long address, unsigned int flags,
- unsigned int *page_mask)
+ struct follow_page_context *ctx)
{
pgd_t *pgd;
struct page *page;
struct mm_struct *mm = vma->vm_mm;

- *page_mask = 0;
+ ctx->page_mask = 0;

/* make this handle hugepd */
page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
@@ -431,7 +432,7 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
return no_page_table(vma, flags);
}

- return follow_p4d_mask(vma, address, pgd, flags, page_mask);
+ return follow_p4d_mask(vma, address, pgd, flags, ctx);
}

static int get_gate_page(struct mm_struct *mm, unsigned long address,
@@ -659,9 +660,9 @@ 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;
- unsigned int page_mask;
+ long ret = 0, i = 0;
struct vm_area_struct *vma = NULL;
+ struct follow_page_context ctx = {};

if (!nr_pages)
return 0;
@@ -691,12 +692,14 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
pages ? &pages[i] : NULL);
if (ret)
return i ? : ret;
- page_mask = 0;
+ ctx.page_mask = 0;
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,
@@ -709,23 +712,26 @@ 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(vma, start, foll_flags, &page_mask);
+
+ page = follow_page_mask(vma, start, foll_flags, &ctx);
if (!page) {
- int ret;
ret = faultin_page(tsk, vma, start, &foll_flags,
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;
}
@@ -737,27 +743,31 @@ 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;
flush_anon_page(vma, page, start);
flush_dcache_page(page);
- page_mask = 0;
+ ctx.page_mask = 0;
}
next_page:
if (vmas) {
vmas[i] = vma;
- page_mask = 0;
+ ctx.page_mask = 0;
}
- page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
+ page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
if (page_increm > nr_pages)
page_increm = nr_pages;
i += page_increm;
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 533f9b00147d..9839bf91b057 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -851,13 +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(unsigned long pfn, struct dev_pagemap **pgmap)
+{
+ struct page *page;
+
+ *pgmap = get_dev_pagemap(pfn, *pgmap);
+ if (!*pgmap)
+ return ERR_PTR(-EFAULT);
+ page = pfn_to_page(pfn);
+ get_page(page);
+ return page;
+}
+
struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
- pmd_t *pmd, int flags)
+ pmd_t *pmd, int flags, struct dev_pagemap **pgmap)
{
unsigned long pfn = pmd_pfn(*pmd);
struct mm_struct *mm = vma->vm_mm;
- struct dev_pagemap *pgmap;
- struct page *page;

assert_spin_locked(pmd_lockptr(mm, pmd));

@@ -886,14 +896,7 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
return ERR_PTR(-EEXIST);

pfn += (addr & ~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(pfn, pgmap);
}

int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
@@ -1000,12 +1003,10 @@ static void touch_pud(struct vm_area_struct *vma, unsigned long addr,
}

struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
- pud_t *pud, int flags)
+ pud_t *pud, int flags, struct dev_pagemap **pgmap)
{
unsigned long pfn = pud_pfn(*pud);
struct mm_struct *mm = vma->vm_mm;
- struct dev_pagemap *pgmap;
- struct page *page;

assert_spin_locked(pud_lockptr(mm, pud));

@@ -1028,14 +1029,7 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
return ERR_PTR(-EEXIST);

pfn += (addr & ~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(pfn, pgmap);
}

int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
diff --git a/mm/nommu.c b/mm/nommu.c
index e4aac33216ae..a795c70cf21e 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1711,9 +1711,9 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,

struct page *follow_page_mask(struct vm_area_struct *vma,
unsigned long address, unsigned int flags,
- unsigned int *page_mask)
+ struct follow_page_context *ctx)
{
- *page_mask = 0;
+ ctx->page_mask = 0;
return NULL;
}

--
2.14.4