[PATCH v4 0/4] mm/gup: page unpining improvements

[PATCH v4 0/4] mm/gup: page unpining improvements

[Joao Martins]

Hey,

This series improves page unpinning, with an eye on improving MR
deregistration for big swaths of memory (which is bound by the page
unpining), particularly:

 1) Decrement the head page by @ntails and thus reducing a lot the number of
atomic operations per compound page. This is done by comparing individual
tail pages heads, and counting number of consecutive tails on which they 
match heads and based on that update head page refcount. Should have a
visible improvement in all page (un)pinners which use compound pages

 2) Introducing a new API for unpinning page ranges (to avoid the trick in the
previous item and be based on math), and use that in RDMA ib_mem_release
(used for mr deregistration).

Performance improvements: unpin_user_pages() for hugetlbfs and THP improves ~3x
(through gup_test) and RDMA MR dereg improves ~4.5x with the new API.
See patches 2 and 4 for those.

These patches used to be in this RFC:

https://lore.kernel.org/linux-mm/20201208172901.17384-1-joao.m.martins@oracle.com/,
"[PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps"

But were moved separately at the suggestion of Jason, given it's applicable
to page unpinning in general. Thanks Jason and John for all the comments.

These patches apply on top of linux-next tag next-20210202.

Suggestions, comments, welcomed as usual.

	Joao

Changelog since,

v3 -> v4:
 * Add the Reviewed-by/Acked-by by Jason on all patches.
 * Add the Reviewed-by by John on the third patch.
 * Fix the wrong mention to get_user_pages()  in
 unpin_user_page_range_dirty_lock()  docs (third patch).

v2 -> v3:
 * Handle compound_order = 1 as well and move subtraction to min_t()
   on patch 3.
 * Remove stale paragraph on patch 3 commit description (John)
 * Rename range_next to compound_range_next() (John)
 * Add John's Reviewed-by on patch 1 (John)
 * Clean and rework compound_next() on patch 1 (John)

v1 -> v2:
 * Prefix macro arguments with __ to avoid collisions with other defines (John)
 * Remove count_tails() and have the logic for the two iterators split into
   range_next() and compound_next() (John)
 * Remove the @range boolean from the iterator helpers (John)
 * Add docs on unpin_user_page_range_dirty_lock() on patch 3 (John)
 * Use unsigned for @i on patch 4 (John)
 * Fix subject line of patch 4 (John)
 * Add John's Reviewed-by on the second patch
 * Fix incorrect use of @nmap and use @sg_nents instead (Jason)

RFC -> v1:
 * Introduce a head/ntails iterator and change unpin_*_pages() to use that,
   inspired by folio iterators (Jason)
 * Introduce an alternative unpin_user_page_range_dirty_lock() to unpin based
   on a consecutive page range without having to walk page arrays (Jason)
 * Use unsigned for number of tails (Jason)


Joao Martins (4):
  mm/gup: add compound page list iterator
  mm/gup: decrement head page once for group of subpages
  mm/gup: add a range variant of unpin_user_pages_dirty_lock()
  RDMA/umem: batch page unpin in __ib_umem_release()

 drivers/infiniband/core/umem.c |  12 ++--
 include/linux/mm.h             |   2 +
 mm/gup.c                       | 117 ++++++++++++++++++++++++++++-----
 3 files changed, 107 insertions(+), 24 deletions(-)

-- 
2.17.1

[PATCH v4 1/4] mm/gup: add compound page list iterator

[Joao Martins]

Add an helper that iterates over head pages in a list of pages. It
essentially counts the tails until the next page to process has a
different head that the current. This is going to be used by
unpin_user_pages() family of functions, to batch the head page refcount
updates once for all passed consecutive tail pages.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
---
 mm/gup.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index e40579624f10..1a709eae2bfd 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -213,6 +213,32 @@ void unpin_user_page(struct page *page)
 }
 EXPORT_SYMBOL(unpin_user_page);
 
+static inline void compound_next(unsigned long i, unsigned long npages,
+				 struct page **list, struct page **head,
+				 unsigned int *ntails)
+{
+	struct page *page;
+	unsigned int nr;
+
+	if (i >= npages)
+		return;
+
+	page = compound_head(list[i]);
+	for (nr = i + 1; nr < npages; nr++) {
+		if (compound_head(list[nr]) != page)
+			break;
+	}
+
+	*head = page;
+	*ntails = nr - i;
+}
+
+#define for_each_compound_head(__i, __list, __npages, __head, __ntails) \
+	for (__i = 0, \
+	     compound_next(__i, __npages, __list, &(__head), &(__ntails)); \
+	     __i < __npages; __i += __ntails, \
+	     compound_next(__i, __npages, __list, &(__head), &(__ntails)))
+
 /**
  * unpin_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
  * @pages:  array of pages to be maybe marked dirty, and definitely released.
-- 
2.17.1

[PATCH v4 2/4] mm/gup: decrement head page once for group of subpages

[Joao Martins]

Rather than decrementing the head page refcount one by one, we
walk the page array and checking which belong to the same
compound_head. Later on we decrement the calculated amount
of references in a single write to the head page. To that
end switch to for_each_compound_head() does most of the work.

set_page_dirty() needs no adjustment as it's a nop for
non-dirty head pages and it doesn't operate on tail pages.

This considerably improves unpinning of pages with THP and
hugetlbfs:

- THP
gup_test -t -m 16384 -r 10 [-L|-a] -S -n 512 -w
PIN_LONGTERM_BENCHMARK (put values): ~87.6k us -> ~23.2k us

- 16G with 1G huge page size
gup_test -f /mnt/huge/file -m 16384 -r 10 [-L|-a] -S -n 512 -w
PIN_LONGTERM_BENCHMARK: (put values): ~87.6k us -> ~27.5k us

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
---
 mm/gup.c | 29 +++++++++++------------------
 1 file changed, 11 insertions(+), 18 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 1a709eae2bfd..384571be2c66 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -265,20 +265,15 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 				 bool make_dirty)
 {
 	unsigned long index;
-
-	/*
-	 * TODO: this can be optimized for huge pages: if a series of pages is
-	 * physically contiguous and part of the same compound page, then a
-	 * single operation to the head page should suffice.
-	 */
+	struct page *head;
+	unsigned int ntails;
 
 	if (!make_dirty) {
 		unpin_user_pages(pages, npages);
 		return;
 	}
 
-	for (index = 0; index < npages; index++) {
-		struct page *page = compound_head(pages[index]);
+	for_each_compound_head(index, pages, npages, head, ntails) {
 		/*
 		 * Checking PageDirty at this point may race with
 		 * clear_page_dirty_for_io(), but that's OK. Two key
@@ -299,9 +294,9 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 		 * written back, so it gets written back again in the
 		 * next writeback cycle. This is harmless.
 		 */
-		if (!PageDirty(page))
-			set_page_dirty_lock(page);
-		unpin_user_page(page);
+		if (!PageDirty(head))
+			set_page_dirty_lock(head);
+		put_compound_head(head, ntails, FOLL_PIN);
 	}
 }
 EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
@@ -318,6 +313,8 @@ EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
 void unpin_user_pages(struct page **pages, unsigned long npages)
 {
 	unsigned long index;
+	struct page *head;
+	unsigned int ntails;
 
 	/*
 	 * If this WARN_ON() fires, then the system *might* be leaking pages (by
@@ -326,13 +323,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
 	 */
 	if (WARN_ON(IS_ERR_VALUE(npages)))
 		return;
-	/*
-	 * TODO: this can be optimized for huge pages: if a series of pages is
-	 * physically contiguous and part of the same compound page, then a
-	 * single operation to the head page should suffice.
-	 */
-	for (index = 0; index < npages; index++)
-		unpin_user_page(pages[index]);
+
+	for_each_compound_head(index, pages, npages, head, ntails)
+		put_compound_head(head, ntails, FOLL_PIN);
 }
 EXPORT_SYMBOL(unpin_user_pages);
 
-- 
2.17.1

[PATCH v4 3/4] mm/gup: add a range variant of unpin_user_pages_dirty_lock()

[Joao Martins]

Add a unpin_user_page_range_dirty_lock() API which takes a starting page
and how many consecutive pages we want to unpin and optionally dirty.

To that end, define another iterator for_each_compound_range()
that operates in page ranges as opposed to page array.

For users (like RDMA mr_dereg) where each sg represents a
contiguous set of pages, we're able to more efficiently unpin
pages without having to supply an array of pages much of what
happens today with unpin_user_pages().

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/mm.h |  2 ++
 mm/gup.c           | 62 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 89fca443e6f1..43f59e4eb760 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1255,6 +1255,8 @@ static inline void put_page(struct page *page)
 void unpin_user_page(struct page *page);
 void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 				 bool make_dirty);
+void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
+				      bool make_dirty);
 void unpin_user_pages(struct page **pages, unsigned long npages);
 
 /**
diff --git a/mm/gup.c b/mm/gup.c
index 384571be2c66..6b6d861727cf 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -213,6 +213,32 @@ void unpin_user_page(struct page *page)
 }
 EXPORT_SYMBOL(unpin_user_page);
 
+static inline void compound_range_next(unsigned long i, unsigned long npages,
+				       struct page **list, struct page **head,
+				       unsigned int *ntails)
+{
+	struct page *next, *page;
+	unsigned int nr = 1;
+
+	if (i >= npages)
+		return;
+
+	next = *list + i;
+	page = compound_head(next);
+	if (PageCompound(page) && compound_order(page) >= 1)
+		nr = min_t(unsigned int,
+			   page + compound_nr(page) - next, npages - i);
+
+	*head = page;
+	*ntails = nr;
+}
+
+#define for_each_compound_range(__i, __list, __npages, __head, __ntails) \
+	for (__i = 0, \
+	     compound_range_next(__i, __npages, __list, &(__head), &(__ntails)); \
+	     __i < __npages; __i += __ntails, \
+	     compound_range_next(__i, __npages, __list, &(__head), &(__ntails)))
+
 static inline void compound_next(unsigned long i, unsigned long npages,
 				 struct page **list, struct page **head,
 				 unsigned int *ntails)
@@ -301,6 +327,42 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 }
 EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
 
+/**
+ * unpin_user_page_range_dirty_lock() - release and optionally dirty
+ * gup-pinned page range
+ *
+ * @page:  the starting page of a range maybe marked dirty, and definitely released.
+ * @npages: number of consecutive pages to release.
+ * @make_dirty: whether to mark the pages dirty
+ *
+ * "gup-pinned page range" refers to a range of pages that has had one of the
+ * pin_user_pages() variants called on that page.
+ *
+ * For the page ranges defined by [page .. page+npages], make that range (or
+ * its head pages, if a compound page) dirty, if @make_dirty is true, and if the
+ * page range was previously listed as clean.
+ *
+ * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
+ * required, then the caller should a) verify that this is really correct,
+ * because _lock() is usually required, and b) hand code it:
+ * set_page_dirty_lock(), unpin_user_page().
+ *
+ */
+void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
+				      bool make_dirty)
+{
+	unsigned long index;
+	struct page *head;
+	unsigned int ntails;
+
+	for_each_compound_range(index, &page, npages, head, ntails) {
+		if (make_dirty && !PageDirty(head))
+			set_page_dirty_lock(head);
+		put_compound_head(head, ntails, FOLL_PIN);
+	}
+}
+EXPORT_SYMBOL(unpin_user_page_range_dirty_lock);
+
 /**
  * unpin_user_pages() - release an array of gup-pinned pages.
  * @pages:  array of pages to be marked dirty and released.
-- 
2.17.1

[PATCH v4 4/4] RDMA/umem: batch page unpin in __ib_umem_release()

[Joao Martins]

Use the newly added unpin_user_page_range_dirty_lock()
for more quickly unpinning a consecutive range of pages
represented as compound pages. This will also calculate
number of pages to unpin (for the tail pages which matching
head page) and thus batch the refcount update.

Running a test program which calls mr reg/unreg on a 1G in size
and measures cost of both operations together (in a guest using rxe)
with THP and hugetlbfs:

Before:
590 rounds in 5.003 sec: 8480.335 usec / round
6898 rounds in 60.001 sec: 8698.367 usec / round

After:
2688 rounds in 5.002 sec: 1860.786 usec / round
32517 rounds in 60.001 sec: 1845.225 usec / round

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Acked-by: Jason Gunthorpe <jgg@nvidia.com>
---
 drivers/infiniband/core/umem.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 2dde99a9ba07..9b607013e2a2 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -47,17 +47,17 @@
 
 static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int dirty)
 {
-	struct sg_page_iter sg_iter;
-	struct page *page;
+	bool make_dirty = umem->writable && dirty;
+	struct scatterlist *sg;
+	unsigned int i;
 
 	if (umem->nmap > 0)
 		ib_dma_unmap_sg(dev, umem->sg_head.sgl, umem->sg_nents,
 				DMA_BIDIRECTIONAL);
 
-	for_each_sg_page(umem->sg_head.sgl, &sg_iter, umem->sg_nents, 0) {
-		page = sg_page_iter_page(&sg_iter);
-		unpin_user_pages_dirty_lock(&page, 1, umem->writable && dirty);
-	}
+	for_each_sg(umem->sg_head.sgl, sg, umem->sg_nents, i)
+		unpin_user_page_range_dirty_lock(sg_page(sg),
+			DIV_ROUND_UP(sg->length, PAGE_SIZE), make_dirty);
 
 	sg_free_table(&umem->sg_head);
 }
-- 
2.17.1

Re: [PATCH v4 0/4] mm/gup: page unpining improvements

[Christoph Hellwig]

On Fri, Feb 12, 2021 at 01:08:39PM +0000, Joao Martins wrote:
> Hey,
> 
> This series improves page unpinning, with an eye on improving MR
> deregistration for big swaths of memory (which is bound by the page
> unpining), particularly:

Can you also take a look at the (bdev and iomap) direct I/O code to
make use of this?  It should really help there, with a much wieder use
than RDMA.

Re: [PATCH v4 0/4] mm/gup: page unpining improvements

[Joao Martins]

On 2/18/21 7:24 AM, Christoph Hellwig wrote:
> On Fri, Feb 12, 2021 at 01:08:39PM +0000, Joao Martins wrote:
>> Hey,
>>
>> This series improves page unpinning, with an eye on improving MR
>> deregistration for big swaths of memory (which is bound by the page
>> unpining), particularly:
> 
> Can you also take a look at the (bdev and iomap) direct I/O code to
> make use of this?  It should really help there, with a much wieder use
> than RDMA.
> 
Perhaps by bdev and iomap direct I/O using this, you were thinking to replace
bio_release_pages() which operates on bvecs and hence releasing contiguous pages
in a bvec at once? e.g. something like from this:

        bio_for_each_segment_all(bvec, bio, iter_all) {
                if (mark_dirty && !PageCompound(bvec->bv_page))
                        set_page_dirty_lock(bvec->bv_page);
                put_page(bvec->bv_page);
        }

(...) to this instead:

	bio_for_each_bvec_all(bvec, bio, i)
		unpin_user_page_range_dirty_lock(bvec->bv_page,
			DIV_ROUND_UP(bvec->bv_len, PAGE_SIZE),
			mark_dirty && !PageCompound(bvec->bv_page));

Re: [PATCH v4 0/4] mm/gup: page unpining improvements

[Joao Martins]

On 2/18/21 3:33 PM, Joao Martins wrote:
> On 2/18/21 7:24 AM, Christoph Hellwig wrote:
>> On Fri, Feb 12, 2021 at 01:08:39PM +0000, Joao Martins wrote:
>>> Hey,
>>>
>>> This series improves page unpinning, with an eye on improving MR
>>> deregistration for big swaths of memory (which is bound by the page
>>> unpining), particularly:
>>
>> Can you also take a look at the (bdev and iomap) direct I/O code to
>> make use of this?  It should really help there, with a much wieder use
>> than RDMA.
>>
> Perhaps by bdev and iomap direct I/O using this, you were thinking to replace
> bio_release_pages() which operates on bvecs and hence releasing contiguous pages
> in a bvec at once? e.g. something like from this:
> 
>         bio_for_each_segment_all(bvec, bio, iter_all) {
>                 if (mark_dirty && !PageCompound(bvec->bv_page))
>                         set_page_dirty_lock(bvec->bv_page);
>                 put_page(bvec->bv_page);
>         }
> 
> (...) to this instead:
> 
> 	bio_for_each_bvec_all(bvec, bio, i)
> 		unpin_user_page_range_dirty_lock(bvec->bv_page,
> 			DIV_ROUND_UP(bvec->bv_len, PAGE_SIZE),
> 			mark_dirty && !PageCompound(bvec->bv_page));
> 

Quick correction: It should be put_user_page_range_dirty_lock() given that unpin is
specific to FOLL_PIN users.

Re: [PATCH v4 0/4] mm/gup: page unpining improvements

[Christoph Hellwig]

On Thu, Feb 18, 2021 at 03:33:39PM +0000, Joao Martins wrote:
> in a bvec at once? e.g. something like from this:
> 
>         bio_for_each_segment_all(bvec, bio, iter_all) {
>                 if (mark_dirty && !PageCompound(bvec->bv_page))
>                         set_page_dirty_lock(bvec->bv_page);
>                 put_page(bvec->bv_page);
>         }
> 
> (...) to this instead:
> 
> 	bio_for_each_bvec_all(bvec, bio, i)
> 		unpin_user_page_range_dirty_lock(bvec->bv_page,
> 			DIV_ROUND_UP(bvec->bv_len, PAGE_SIZE),
> 			mark_dirty && !PageCompound(bvec->bv_page));

Yes, like that modulo the fix in your reply and any other fixes.