Hi,
Jan and Kirill: I've tentatively removed your review and ACK,
respectively, for patch 12 (the last dump_page patch), because even
though they are logically the same as what you reviewed in v5, the
base is Matthew's new patch instead of my earlier patch. (Trying to err
on the side of caution with these tags.)
There is a git repo and branch, for convenience in reviewing:
[email protected]:johnhubbard/linux.git track_user_pages_v6
============================================================
Changes since v5:
* Rebased onto Linux 5.6.0-rc1.
* Swapped in Matthew Wilcox's more comprehensive dump_page() patch, and
moved it later in this series so that it immediately precedes my
subsequent dump_page() patch, for slightly easier reviews and commit
log history.
* Fixed "the last bug!" in the /proc/vmstat patch, by moving the
mod_node_page_state() call in put_compound_page() so that it only
happens in the FOLL_PIN case.
* Added a couple more ACKs from Kirill.
* Tweaked the "Future steps" in this cover letter to add a little
detail about what comes next.
============================================================
Changes since v4:
* Added documentation about the huge page behavior of the new
/proc/vmstat items.
* Added a missing mode_node_page_state() call to put_compound_head().
* Fixed a tracepoint call in page_ref_sub_return().
* Added a trailing underscore to a URL in pin_user_pages.rst, to fix
a broken generated link.
* Added ACKs and reviewed-by's from Jan Kara and Kirill Shutemov.
* Rebased onto today's linux.git, and
* I am experimenting here with "git format-patch --base=<commit>".
This generated the "base-commit:" tag you'll see at the end of this
cover letter. I was inspired to do so after trying out a new
get-lore-mbox.py tool (it's very nice), mentioned in a recent LWN
article (https://lwn.net/Articles/811528/ ). That tool relies on the
base-commit tag for some things.
============================================================
Changes since v3:
* Rebased onto latest linux.git
* Added ACKs and reviewed-by's from Kirill Shutemov and Jan Kara.
* /proc/vmstat:
* Renamed items, after realizing that I hate the previous names:
nr_foll_pin_requested --> nr_foll_pin_acquired
nr_foll_pin_returned --> nr_foll_pin_released
* Removed the CONFIG_DEBUG_VM guard, and collapsed away a wrapper
routine: now just calls mod_node_page_state() directly.
* Tweaked the WARN_ON_ONCE() statements in mm/hugetlb.c to be more
informative, and added comments above them as well.
* Fixed gup_benchmark: signed int --> unsigned long.
* One or two minor formatting changes.
============================================================
Changes since v2:
* Rebased onto linux.git, because the akpm tree for 5.6 has been merged.
* Split the tracking patch into even more patches, as requested.
* Merged Matthew Wilcox's dump_page() changes into mine, as part of the
first patch.
* Renamed: page_dma_pinned() --> page_maybe_dma_pinned(), in response to
Kirill Shutemov's review.
* Moved a WARN to the top of a routine, and fixed a typo in the commit
description of patch #7, also as suggested by Kirill.
============================================================
Changes since v1:
* Split the tracking patch into 6 smaller patches
* Rebased onto today's linux-next/akpm (there weren't any conflicts).
* Fixed an "unsigned int" vs. "int" problem in gup_benchmark, reported
by Nathan Chancellor. (I don't see it in my local builds, probably
because they use gcc, but an LLVM test found the mismatch.)
* Fixed a huge page pincount problem (add/subtract vs.
increment/decrement), spotted by Jan Kara.
============================================================
There is a reasonable case to be made for merging two of the patches
(patches 7 and 8), given that patch 7 provides tracking that has upper
limits on the number of pins that can be done with huge pages. Let me
know if anyone wants those merged, but unless there is some weird chance
of someone grabbing patch 7 and not patch 8, I don't really see the
need. Meanwhile, it's easier to review in this form.
Also, patch 3 has been revived. Earlier reviewers asked for it to be
merged into the tracking patch (one cannot please everyone, heh), but
now it's back out on it's own.
This activates tracking of FOLL_PIN pages. This is in support of fixing
the get_user_pages()+DMA problem described in [1]-[4].
FOLL_PIN support is now in the main linux tree. However, the
patch to use FOLL_PIN to track pages was *not* submitted, because Leon
saw an RDMA test suite failure that involved (I think) page refcount
overflows when huge pages were used.
This patch definitively solves that kind of overflow problem, by adding
an exact pincount, for compound pages (of order > 1), in the 3rd struct
page of a compound page. If available, that form of pincounting is used,
instead of the GUP_PIN_COUNTING_BIAS approach. Thanks again to Jan Kara
for that idea.
Other interesting changes:
* dump_page(): added one, or two new things to report for compound
pages: head refcount (for all compound pages), and map_pincount (for
compound pages of order > 1).
* Documentation/core-api/pin_user_pages.rst: removed the "TODO" for the
huge page refcount upper limit problems, and added notes about how it
works now. Also added a note about the dump_page() enhancements.
* Added some comments in gup.c and mm.h, to explain that there are two
ways to count pinned pages: exact (for compound pages of order > 1)
and fuzzy (GUP_PIN_COUNTING_BIAS: for all other pages).
============================================================
General notes about the tracking patch:
This is a prerequisite to solving the problem of proper interactions
between file-backed pages, and [R]DMA activities, as discussed in [1],
[2], [3], [4] and in a remarkable number of email threads since about
2017. :)
In contrast to earlier approaches, the page tracking can be
incrementally applied to the kernel call sites that, until now, have
been simply calling get_user_pages() ("gup"). In other words, opt-in by
changing from this:
get_user_pages() (sets FOLL_GET)
put_page()
to this:
pin_user_pages() (sets FOLL_PIN)
unpin_user_page()
============================================================
Future steps:
* Convert more subsystems from get_user_pages() to pin_user_pages().
The first probably needs to be bio/biovecs, because any filesystem
testing is too difficult without those in place.
* Change VFS and filesystems to respond appropriately when encountering
dma-pinned pages.
* Work with Ira and others to connect this all up with file system
leases.
[1] Some slow progress on get_user_pages() (Apr 2, 2019):
https://lwn.net/Articles/784574/
[2] DMA and get_user_pages() (LPC: Dec 12, 2018):
https://lwn.net/Articles/774411/
[3] The trouble with get_user_pages() (Apr 30, 2018):
https://lwn.net/Articles/753027/
[4] LWN kernel index: get_user_pages()
https://lwn.net/Kernel/Index/#Memory_management-get_user_pages
John Hubbard (11):
mm/gup: split get_user_pages_remote() into two routines
mm/gup: pass a flags arg to __gup_device_* functions
mm: introduce page_ref_sub_return()
mm/gup: pass gup flags to two more routines
mm/gup: require FOLL_GET for get_user_pages_fast()
mm/gup: track FOLL_PIN pages
mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages
mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting
mm/gup_benchmark: support pin_user_pages() and related calls
selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN
coverage
mm: dump_page(): additional diagnostics for huge pinned pages
Matthew Wilcox (Oracle) (1):
mm: Improve dump_page() for compound pages
Documentation/core-api/pin_user_pages.rst | 86 ++--
include/linux/mm.h | 108 ++++-
include/linux/mm_types.h | 7 +-
include/linux/mmzone.h | 2 +
include/linux/page_ref.h | 9 +
mm/debug.c | 44 +-
mm/gup.c | 451 ++++++++++++++++-----
mm/gup_benchmark.c | 71 +++-
mm/huge_memory.c | 29 +-
mm/hugetlb.c | 60 ++-
mm/page_alloc.c | 2 +
mm/rmap.c | 6 +
mm/vmstat.c | 2 +
tools/testing/selftests/vm/gup_benchmark.c | 15 +-
tools/testing/selftests/vm/run_vmtests | 22 +
15 files changed, 734 insertions(+), 180 deletions(-)
base-commit: bb6d3fb354c5ee8d6bde2d576eb7220ea09862b9
--
2.25.0
In preparation for an upcoming patch, send gup flags args to two more
routines: put_compound_head(), and undo_dev_pagemap().
Acked-by: Kirill A. Shutemov <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: John Hubbard <[email protected]>
---
mm/gup.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index 9e117998274c..e5f75e886663 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1870,6 +1870,7 @@ static inline pte_t gup_get_pte(pte_t *ptep)
#endif /* CONFIG_GUP_GET_PTE_LOW_HIGH */
static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start,
+ unsigned int flags,
struct page **pages)
{
while ((*nr) - nr_start) {
@@ -1909,7 +1910,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
if (unlikely(!pgmap)) {
- undo_dev_pagemap(nr, nr_start, pages);
+ undo_dev_pagemap(nr, nr_start, flags, pages);
goto pte_unmap;
}
} else if (pte_special(pte))
@@ -1974,7 +1975,7 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
pgmap = get_dev_pagemap(pfn, pgmap);
if (unlikely(!pgmap)) {
- undo_dev_pagemap(nr, nr_start, pages);
+ undo_dev_pagemap(nr, nr_start, flags, pages);
return 0;
}
SetPageReferenced(page);
@@ -2001,7 +2002,7 @@ static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
return 0;
if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
- undo_dev_pagemap(nr, nr_start, pages);
+ undo_dev_pagemap(nr, nr_start, flags, pages);
return 0;
}
return 1;
@@ -2019,7 +2020,7 @@ static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
return 0;
if (unlikely(pud_val(orig) != pud_val(*pudp))) {
- undo_dev_pagemap(nr, nr_start, pages);
+ undo_dev_pagemap(nr, nr_start, flags, pages);
return 0;
}
return 1;
@@ -2053,7 +2054,7 @@ static int record_subpages(struct page *page, unsigned long addr,
return nr;
}
-static void put_compound_head(struct page *page, int refs)
+static void put_compound_head(struct page *page, int refs, unsigned int flags)
{
VM_BUG_ON_PAGE(page_ref_count(page) < refs, page);
/*
@@ -2103,7 +2104,7 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
return 0;
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
- put_compound_head(head, refs);
+ put_compound_head(head, refs, flags);
return 0;
}
@@ -2163,7 +2164,7 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
return 0;
if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
- put_compound_head(head, refs);
+ put_compound_head(head, refs, flags);
return 0;
}
@@ -2197,7 +2198,7 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
return 0;
if (unlikely(pud_val(orig) != pud_val(*pudp))) {
- put_compound_head(head, refs);
+ put_compound_head(head, refs, flags);
return 0;
}
@@ -2226,7 +2227,7 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
return 0;
if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
- put_compound_head(head, refs);
+ put_compound_head(head, refs, flags);
return 0;
}
--
2.25.0
Up until now, gup_benchmark supported testing of the
following kernel functions:
* get_user_pages(): via the '-U' command line option
* get_user_pages_longterm(): via the '-L' command line option
* get_user_pages_fast(): as the default (no options required)
Add test coverage for the new corresponding pin_*() functions:
* pin_user_pages_fast(): via the '-a' command line option
* pin_user_pages(): via the '-b' command line option
Also, add an option for clarity: '-u' for what is now (still) the
default choice: get_user_pages_fast().
Also, for the commands that set FOLL_PIN, verify that the pages
really are dma-pinned, via the new is_dma_pinned() routine.
Those commands are:
PIN_FAST_BENCHMARK : calls pin_user_pages_fast()
PIN_BENCHMARK : calls pin_user_pages()
In between the calls to pin_*() and unpin_user_pages(),
check each page: if page_maybe_dma_pinned() returns false, then
WARN and return.
Do this outside of the benchmark timestamps, so that it doesn't
affect reported times.
Reviewed-by: Ira Weiny <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Signed-off-by: John Hubbard <[email protected]>
---
mm/gup_benchmark.c | 71 ++++++++++++++++++++--
tools/testing/selftests/vm/gup_benchmark.c | 15 ++++-
2 files changed, 80 insertions(+), 6 deletions(-)
diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
index 8dba38e79a9f..be690fa66a46 100644
--- a/mm/gup_benchmark.c
+++ b/mm/gup_benchmark.c
@@ -8,6 +8,8 @@
#define GUP_FAST_BENCHMARK _IOWR('g', 1, struct gup_benchmark)
#define GUP_LONGTERM_BENCHMARK _IOWR('g', 2, struct gup_benchmark)
#define GUP_BENCHMARK _IOWR('g', 3, struct gup_benchmark)
+#define PIN_FAST_BENCHMARK _IOWR('g', 4, struct gup_benchmark)
+#define PIN_BENCHMARK _IOWR('g', 5, struct gup_benchmark)
struct gup_benchmark {
__u64 get_delta_usec;
@@ -19,6 +21,48 @@ struct gup_benchmark {
__u64 expansion[10]; /* For future use */
};
+static void put_back_pages(unsigned int cmd, struct page **pages,
+ unsigned long nr_pages)
+{
+ unsigned long i;
+
+ switch (cmd) {
+ case GUP_FAST_BENCHMARK:
+ case GUP_LONGTERM_BENCHMARK:
+ case GUP_BENCHMARK:
+ for (i = 0; i < nr_pages; i++)
+ put_page(pages[i]);
+ break;
+
+ case PIN_FAST_BENCHMARK:
+ case PIN_BENCHMARK:
+ unpin_user_pages(pages, nr_pages);
+ break;
+ }
+}
+
+static void verify_dma_pinned(unsigned int cmd, struct page **pages,
+ unsigned long nr_pages)
+{
+ unsigned long i;
+ struct page *page;
+
+ switch (cmd) {
+ case PIN_FAST_BENCHMARK:
+ case PIN_BENCHMARK:
+ for (i = 0; i < nr_pages; i++) {
+ page = pages[i];
+ if (WARN(!page_maybe_dma_pinned(page),
+ "pages[%lu] is NOT dma-pinned\n", i)) {
+
+ dump_page(page, "gup_benchmark failure");
+ break;
+ }
+ }
+ break;
+ }
+}
+
static int __gup_benchmark_ioctl(unsigned int cmd,
struct gup_benchmark *gup)
{
@@ -66,6 +110,14 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
nr = get_user_pages(addr, nr, gup->flags, pages + i,
NULL);
break;
+ case PIN_FAST_BENCHMARK:
+ nr = pin_user_pages_fast(addr, nr, gup->flags,
+ pages + i);
+ break;
+ case PIN_BENCHMARK:
+ nr = pin_user_pages(addr, nr, gup->flags, pages + i,
+ NULL);
+ break;
default:
kvfree(pages);
ret = -EINVAL;
@@ -78,15 +130,22 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
}
end_time = ktime_get();
+ /* Shifting the meaning of nr_pages: now it is actual number pinned: */
+ nr_pages = i;
+
gup->get_delta_usec = ktime_us_delta(end_time, start_time);
gup->size = addr - gup->addr;
+ /*
+ * Take an un-benchmark-timed moment to verify DMA pinned
+ * state: print a warning if any non-dma-pinned pages are found:
+ */
+ verify_dma_pinned(cmd, pages, nr_pages);
+
start_time = ktime_get();
- for (i = 0; i < nr_pages; i++) {
- if (!pages[i])
- break;
- put_page(pages[i]);
- }
+
+ put_back_pages(cmd, pages, nr_pages);
+
end_time = ktime_get();
gup->put_delta_usec = ktime_us_delta(end_time, start_time);
@@ -105,6 +164,8 @@ static long gup_benchmark_ioctl(struct file *filep, unsigned int cmd,
case GUP_FAST_BENCHMARK:
case GUP_LONGTERM_BENCHMARK:
case GUP_BENCHMARK:
+ case PIN_FAST_BENCHMARK:
+ case PIN_BENCHMARK:
break;
default:
return -EINVAL;
diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c
index 389327e9b30a..43b4dfe161a2 100644
--- a/tools/testing/selftests/vm/gup_benchmark.c
+++ b/tools/testing/selftests/vm/gup_benchmark.c
@@ -18,6 +18,10 @@
#define GUP_LONGTERM_BENCHMARK _IOWR('g', 2, struct gup_benchmark)
#define GUP_BENCHMARK _IOWR('g', 3, struct gup_benchmark)
+/* Similar to above, but use FOLL_PIN instead of FOLL_GET. */
+#define PIN_FAST_BENCHMARK _IOWR('g', 4, struct gup_benchmark)
+#define PIN_BENCHMARK _IOWR('g', 5, struct gup_benchmark)
+
/* Just the flags we need, copied from mm.h: */
#define FOLL_WRITE 0x01 /* check pte is writable */
@@ -40,8 +44,14 @@ int main(int argc, char **argv)
char *file = "/dev/zero";
char *p;
- while ((opt = getopt(argc, argv, "m:r:n:f:tTLUwSH")) != -1) {
+ while ((opt = getopt(argc, argv, "m:r:n:f:abtTLUuwSH")) != -1) {
switch (opt) {
+ case 'a':
+ cmd = PIN_FAST_BENCHMARK;
+ break;
+ case 'b':
+ cmd = PIN_BENCHMARK;
+ break;
case 'm':
size = atoi(optarg) * MB;
break;
@@ -63,6 +73,9 @@ int main(int argc, char **argv)
case 'U':
cmd = GUP_BENCHMARK;
break;
+ case 'u':
+ cmd = GUP_FAST_BENCHMARK;
+ break;
case 'w':
write = 1;
break;
--
2.25.0