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mm/gup: cache dev_pagemap while pinning pages
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Getting 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 while getting user
pages.  The gup_benchmark kernel self test reports this reduces time to
get user pages to as low as 1/3 of the previous time.

Link: http://lkml.kernel.org/r/20181012173040.15669-1-keith.busch@intel.com
Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@torvalds
Keith Busch authored and torvalds committed Oct 26, 2018
1 parent 9fd61bc commit df06b37
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Showing 5 changed files with 79 additions and 73 deletions.
8 changes: 4 additions & 4 deletions include/linux/huge_mm.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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);

Expand Down Expand Up @@ -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;
}
Expand Down
12 changes: 2 additions & 10 deletions include/linux/mm.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2536,16 +2536,8 @@ static inline vm_fault_t vmf_error(int err)
return VM_FAULT_SIGBUS;
}

struct page *follow_page_mask(struct vm_area_struct *vma,
unsigned long address, unsigned int foll_flags,
unsigned int *page_mask);

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 *follow_page(struct vm_area_struct *vma, unsigned long address,
unsigned int foll_flags);

#define FOLL_WRITE 0x01 /* check pte is writable */
#define FOLL_TOUCH 0x02 /* mark page accessed */
Expand Down
110 changes: 65 additions & 45 deletions mm/gup.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,11 @@

#include "internal.h"

struct follow_page_context {
struct dev_pagemap *pgmap;
unsigned int page_mask;
};

static struct page *no_page_table(struct vm_area_struct *vma,
unsigned int flags)
{
Expand Down Expand Up @@ -71,10 +76,10 @@ 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;
Expand Down Expand Up @@ -116,8 +121,8 @@ 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;
Expand Down Expand Up @@ -152,15 +157,8 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
goto retry;
}

if (flags & FOLL_GET) {
if (flags & FOLL_GET)
get_page(page);

/* drop the pgmap reference now that we hold the page */
if (pgmap) {
put_dev_pagemap(pgmap);
pgmap = NULL;
}
}
if (flags & FOLL_TOUCH) {
if ((flags & FOLL_WRITE) &&
!pte_dirty(pte) && !PageDirty(page))
Expand Down Expand Up @@ -210,7 +208,8 @@ 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;
Expand Down Expand Up @@ -258,13 +257,13 @@ 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);
Expand All @@ -284,7 +283,7 @@ 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;
Expand All @@ -307,18 +306,18 @@ 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;
Expand All @@ -344,21 +343,21 @@ 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;
}
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;
Expand All @@ -378,7 +377,7 @@ 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);
}

/**
Expand All @@ -396,13 +395,13 @@ 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);
Expand Down Expand Up @@ -431,7 +430,19 @@ 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);
}

struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
unsigned int foll_flags)
{
struct follow_page_context ctx = { NULL };
struct page *page;

page = follow_page_mask(vma, address, foll_flags, &ctx);
if (ctx.pgmap)
put_dev_pagemap(ctx.pgmap);
return page;
}

static int get_gate_page(struct mm_struct *mm, unsigned long address,
Expand Down Expand Up @@ -659,9 +670,9 @@ 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 = { NULL };

if (!nr_pages)
return 0;
Expand Down Expand Up @@ -691,12 +702,14 @@ 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,
Expand All @@ -709,23 +722,26 @@ 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;
}
Expand All @@ -737,27 +753,31 @@ 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,
Expand Down
16 changes: 6 additions & 10 deletions mm/huge_memory.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -852,11 +852,10 @@ static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
}

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));
Expand Down Expand Up @@ -886,12 +885,11 @@ 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)
*pgmap = get_dev_pagemap(pfn, *pgmap);
if (!*pgmap)
return ERR_PTR(-EFAULT);
page = pfn_to_page(pfn);
get_page(page);
put_dev_pagemap(pgmap);

return page;
}
Expand Down Expand Up @@ -1000,11 +998,10 @@ 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));
Expand All @@ -1028,12 +1025,11 @@ 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)
*pgmap = get_dev_pagemap(pfn, *pgmap);
if (!*pgmap)
return ERR_PTR(-EFAULT);
page = pfn_to_page(pfn);
get_page(page);
put_dev_pagemap(pgmap);

return page;
}
Expand Down
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