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Date: Sun, 3 Feb 2019 21:21:34 -0800
From: john.hubbard@...il.com
To: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc: Al Viro <viro@...iv.linux.org.uk>,
Christian Benvenuti <benve@...co.com>,
Christoph Hellwig <hch@...radead.org>,
Christopher Lameter <cl@...ux.com>,
Dan Williams <dan.j.williams@...el.com>,
Dave Chinner <david@...morbit.com>,
Dennis Dalessandro <dennis.dalessandro@...el.com>,
Doug Ledford <dledford@...hat.com>, Jan Kara <jack@...e.cz>,
Jason Gunthorpe <jgg@...pe.ca>,
Jerome Glisse <jglisse@...hat.com>,
Matthew Wilcox <willy@...radead.org>,
Michal Hocko <mhocko@...nel.org>,
Mike Rapoport <rppt@...ux.ibm.com>,
Mike Marciniszyn <mike.marciniszyn@...el.com>,
Ralph Campbell <rcampbell@...dia.com>,
Tom Talpey <tom@...pey.com>,
LKML <linux-kernel@...r.kernel.org>,
linux-fsdevel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>
Subject: [PATCH 5/6] mm/gup: /proc/vmstat support for get/put user pages
From: John Hubbard <jhubbard@...dia.com>
Add five new /proc/vmstat items, to provide some
visibility into what get_user_pages() and put_user_page()
are doing.
After booting and running fio (https://github.com/axboe/fio)
a few times on an NVMe device, as a way to get lots of
get_user_pages_fast() calls, the counters look like this:
$ cat /proc/vmstat |grep gup
nr_gup_slow_pages_requested 21319
nr_gup_fast_pages_requested 11533792
nr_gup_fast_page_backoffs 0
nr_gup_page_count_overflows 0
nr_gup_pages_returned 11555104
Interpretation of the above:
Total gup requests (slow + fast): 11555111
Total put_user_page calls: 11555104
This shows 7 more calls to get_user_pages(), than to
put_user_page(). That may, or may not, represent a
problem worth investigating.
Normally, those last two numbers should be equal, but a
couple of things may cause them to differ:
1) Inherent race condition in reading /proc/vmstat values.
2) Bugs at any of the get_user_pages*() call sites. Those
sites need to match get_user_pages() and put_user_page() calls.
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
include/linux/mmzone.h | 5 +++++
mm/gup.c | 20 ++++++++++++++++++++
mm/swap.c | 1 +
mm/vmstat.c | 5 +++++
4 files changed, 31 insertions(+)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 842f9189537b..f20c14958a2b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -183,6 +183,11 @@ enum node_stat_item {
NR_DIRTIED, /* page dirtyings since bootup */
NR_WRITTEN, /* page writings since bootup */
NR_KERNEL_MISC_RECLAIMABLE, /* reclaimable non-slab kernel pages */
+ NR_GUP_SLOW_PAGES_REQUESTED, /* via: get_user_pages() */
+ NR_GUP_FAST_PAGES_REQUESTED, /* via: get_user_pages_fast() */
+ NR_GUP_FAST_PAGE_BACKOFFS, /* gup_fast() lost to page_mkclean() */
+ NR_GUP_PAGE_COUNT_OVERFLOWS, /* gup count overflowed: gup() failed */
+ NR_GUP_PAGES_RETURNED, /* via: put_user_page() */
NR_VM_NODE_STAT_ITEMS
};
diff --git a/mm/gup.c b/mm/gup.c
index 3291da342f9c..848ee7899831 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -37,6 +37,8 @@ int get_gup_pin_page(struct page *page)
page = compound_head(page);
if (page_ref_count(page) >= (UINT_MAX - GUP_PIN_COUNTING_BIAS)) {
+ mod_node_page_state(page_pgdat(page),
+ NR_GUP_PAGE_COUNT_OVERFLOWS, 1);
WARN_ONCE(1, "get_user_pages pin count overflowed");
return -EOVERFLOW;
}
@@ -184,6 +186,8 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
page = ERR_PTR(ret);
goto out;
}
+ mod_node_page_state(page_pgdat(page),
+ NR_GUP_SLOW_PAGES_REQUESTED, 1);
}
if (flags & FOLL_TOUCH) {
if ((flags & FOLL_WRITE) &&
@@ -527,6 +531,8 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
ret = get_gup_pin_page(*page);
if (ret)
goto unmap;
+
+ mod_node_page_state(page_pgdat(*page), NR_GUP_SLOW_PAGES_REQUESTED, 1);
out:
ret = 0;
unmap:
@@ -1461,7 +1467,12 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
if (!page_cache_gup_pin_speculative(head))
goto pte_unmap;
+ mod_node_page_state(page_pgdat(head),
+ NR_GUP_FAST_PAGES_REQUESTED, 1);
+
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
+ mod_node_page_state(page_pgdat(head),
+ NR_GUP_FAST_PAGE_BACKOFFS, 1);
put_user_page(head);
goto pte_unmap;
}
@@ -1522,6 +1533,9 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
return 0;
}
+ mod_node_page_state(page_pgdat(page),
+ NR_GUP_FAST_PAGES_REQUESTED, 1);
+
(*nr)++;
pfn++;
} while (addr += PAGE_SIZE, addr != end);
@@ -1607,6 +1621,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
return 0;
}
+ mod_node_page_state(page_pgdat(head), NR_GUP_FAST_PAGES_REQUESTED, 1);
+
if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
*nr -= refs;
put_user_page(head);
@@ -1644,6 +1660,8 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
return 0;
}
+ mod_node_page_state(page_pgdat(head), NR_GUP_FAST_PAGES_REQUESTED, 1);
+
if (unlikely(pud_val(orig) != pud_val(*pudp))) {
*nr -= refs;
put_user_page(head);
@@ -1680,6 +1698,8 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
return 0;
}
+ mod_node_page_state(page_pgdat(head), NR_GUP_FAST_PAGES_REQUESTED, 1);
+
if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
*nr -= refs;
put_user_page(head);
diff --git a/mm/swap.c b/mm/swap.c
index 39b0ddd35933..49e192f242d4 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -150,6 +150,7 @@ void put_user_page(struct page *page)
VM_BUG_ON_PAGE(page_ref_count(page) < GUP_PIN_COUNTING_BIAS, page);
+ mod_node_page_state(page_pgdat(page), NR_GUP_PAGES_RETURNED, 1);
page_ref_sub(page, GUP_PIN_COUNTING_BIAS);
}
EXPORT_SYMBOL(put_user_page);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 83b30edc2f7f..18a1a4a2dd29 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1164,6 +1164,11 @@ const char * const vmstat_text[] = {
"nr_dirtied",
"nr_written",
"nr_kernel_misc_reclaimable",
+ "nr_gup_slow_pages_requested",
+ "nr_gup_fast_pages_requested",
+ "nr_gup_fast_page_backoffs",
+ "nr_gup_page_count_overflows",
+ "nr_gup_pages_returned",
/* enum writeback_stat_item counters */
"nr_dirty_threshold",
--
2.20.1
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