+ mm-gup-proc-vmstat-pin_user_pages-foll_pin-reporting.patch added to -mm tree

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The patch titled
     Subject: mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting
has been added to the -mm tree.  Its filename is
     mm-gup-proc-vmstat-pin_user_pages-foll_pin-reporting.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-gup-proc-vmstat-pin_user_pages-foll_pin-reporting.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-gup-proc-vmstat-pin_user_pages-foll_pin-reporting.patch

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------------------------------------------------------
From: John Hubbard <jhubbard@xxxxxxxxxx>
Subject: mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting

Now that pages are "DMA-pinned" via pin_user_page*(), and unpinned via
unpin_user_pages*(), we need some visibility into whether all of this is
working correctly.

Add two new fields to /proc/vmstat:

    nr_foll_pin_acquired
    nr_foll_pin_released

These are documented in Documentation/core-api/pin_user_pages.rst.  They
represent the number of pages (since boot time) that have been pinned
("nr_foll_pin_acquired") and unpinned ("nr_foll_pin_released"), via
pin_user_pages*() and unpin_user_pages*().

In the absence of long-running DMA or RDMA operations that hold pages
pinned, the above two fields will normally be equal to each other.

Also: update Documentation/core-api/pin_user_pages.rst, to remove an
earlier (now confirmed untrue) claim about a performance problem with
/proc/vmstat.

Also: update Documentation/core-api/pin_user_pages.rst to rename the new
/proc/vmstat entries, to the names listed here.

Link: http://lkml.kernel.org/r/20200211001536.1027652-9-jhubbard@xxxxxxxxxx
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 Documentation/core-api/pin_user_pages.rst |   33 ++++++++++++++++----
 include/linux/mmzone.h                    |    2 +
 mm/gup.c                                  |   13 +++++++
 mm/vmstat.c                               |    2 +
 4 files changed, 45 insertions(+), 5 deletions(-)

--- a/Documentation/core-api/pin_user_pages.rst~mm-gup-proc-vmstat-pin_user_pages-foll_pin-reporting
+++ a/Documentation/core-api/pin_user_pages.rst
@@ -208,12 +208,35 @@ has the following new calls to exercise
 You can monitor how many total dma-pinned pages have been acquired and released
 since the system was booted, via two new /proc/vmstat entries: ::
 
-    /proc/vmstat/nr_foll_pin_requested
-    /proc/vmstat/nr_foll_pin_requested
+    /proc/vmstat/nr_foll_pin_acquired
+    /proc/vmstat/nr_foll_pin_released
 
-Those are both going to show zero, unless CONFIG_DEBUG_VM is set. This is
-because there is a noticeable performance drop in unpin_user_page(), when they
-are activated.
+Under normal conditions, these two values will be equal unless there are any
+long-term [R]DMA pins in place, or during pin/unpin transitions.
+
+* nr_foll_pin_acquired: This is the number of logical pins that have been
+  acquired since the system was powered on. For huge pages, the head page is
+  pinned once for each page (head page and each tail page) within the huge page.
+  This follows the same sort of behavior that get_user_pages() uses for huge
+  pages: the head page is refcounted once for each tail or head page in the huge
+  page, when get_user_pages() is applied to a huge page.
+
+* nr_foll_pin_released: The number of logical pins that have been released since
+  the system was powered on. Note that pages are released (unpinned) on a
+  PAGE_SIZE granularity, even if the original pin was applied to a huge page.
+  Becaused of the pin count behavior described above in "nr_foll_pin_acquired",
+  the accounting balances out, so that after doing this::
+
+    pin_user_pages(huge_page);
+    for (each page in huge_page)
+        unpin_user_page(page);
+
+...the following is expected::
+
+    nr_foll_pin_released == nr_foll_pin_acquired
+
+(...unless it was already out of balance due to a long-term RDMA pin being in
+place.)
 
 References
 ==========
--- a/include/linux/mmzone.h~mm-gup-proc-vmstat-pin_user_pages-foll_pin-reporting
+++ a/include/linux/mmzone.h
@@ -243,6 +243,8 @@ 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_FOLL_PIN_ACQUIRED,	/* via: pin_user_page(), gup flag: FOLL_PIN */
+	NR_FOLL_PIN_RELEASED,	/* pages returned via unpin_user_page() */
 	NR_VM_NODE_STAT_ITEMS
 };
 
--- a/mm/gup.c~mm-gup-proc-vmstat-pin_user_pages-foll_pin-reporting
+++ a/mm/gup.c
@@ -86,6 +86,8 @@ static __maybe_unused struct page *try_g
 	if (flags & FOLL_GET)
 		return try_get_compound_head(page, refs);
 	else if (flags & FOLL_PIN) {
+		int orig_refs = refs;
+
 		/*
 		 * When pinning a compound page of order > 1 (which is what
 		 * hpage_pincount_available() checks for), use an exact count to
@@ -104,6 +106,9 @@ static __maybe_unused struct page *try_g
 		if (hpage_pincount_available(page))
 			hpage_pincount_add(page, refs);
 
+		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED,
+				    orig_refs);
+
 		return page;
 	}
 
@@ -158,6 +163,8 @@ bool __must_check try_grab_page(struct p
 		 * once, so that the page really is pinned.
 		 */
 		page_ref_add(page, refs);
+
+		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1);
 	}
 
 	return true;
@@ -178,6 +185,7 @@ static bool __unpin_devmap_managed_user_
 
 	count = page_ref_sub_return(page, refs);
 
+	mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1);
 	/*
 	 * devmap page refcounts are 1-based, rather than 0-based: if
 	 * refcount is 1, then the page is free and the refcount is
@@ -228,6 +236,8 @@ void unpin_user_page(struct page *page)
 
 	if (page_ref_sub_and_test(page, refs))
 		__put_page(page);
+
+	mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1);
 }
 EXPORT_SYMBOL(unpin_user_page);
 
@@ -2259,6 +2269,9 @@ static int record_subpages(struct page *
 static void put_compound_head(struct page *page, int refs, unsigned int flags)
 {
 	if (flags & FOLL_PIN) {
+		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED,
+				    refs);
+
 		if (hpage_pincount_available(page))
 			hpage_pincount_sub(page, refs);
 		else
--- a/mm/vmstat.c~mm-gup-proc-vmstat-pin_user_pages-foll_pin-reporting
+++ a/mm/vmstat.c
@@ -1168,6 +1168,8 @@ const char * const vmstat_text[] = {
 	"nr_dirtied",
 	"nr_written",
 	"nr_kernel_misc_reclaimable",
+	"nr_foll_pin_acquired",
+	"nr_foll_pin_released",
 
 	/* enum writeback_stat_item counters */
 	"nr_dirty_threshold",
_

Patches currently in -mm which might be from jhubbard@xxxxxxxxxx are

mm-gup-split-get_user_pages_remote-into-two-routines.patch
mm-gup-pass-a-flags-arg-to-__gup_device_-functions.patch
mm-introduce-page_ref_sub_return.patch
mm-gup-pass-gup-flags-to-two-more-routines.patch
mm-gup-require-foll_get-for-get_user_pages_fast.patch
mm-gup-track-foll_pin-pages.patch
mm-gup-page-hpage_pinned_refcount-exact-pin-counts-for-huge-pages.patch
mm-gup-proc-vmstat-pin_user_pages-foll_pin-reporting.patch
mm-gup_benchmark-support-pin_user_pages-and-related-calls.patch
selftests-vm-run_vmtests-invoke-gup_benchmark-with-basic-foll_pin-coverage.patch
mm-dump_page-additional-diagnostics-for-huge-pinned-pages.patch





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