linux-kernel - Re: get_zone_device_page() in get_page() and page_cache_get

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Date:   Tue, 25 Apr 2017 16:19:04 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Linux MM <linux-mm@...ck.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Steve Capper <steve.capper@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bp@...en8.de>, Rik van Riel <riel@...hat.com>,
        Dann Frazier <dann.frazier@...onical.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.cz>,
        linux-tip-commits@...r.kernel.org
Subject: Re: get_zone_device_page() in get_page() and
 page_cache_get_speculative()

On Mon, Apr 24, 2017 at 11:41:51AM -0700, Dan Williams wrote:
> On Mon, Apr 24, 2017 at 11:25 AM, Kirill A. Shutemov
> <kirill.shutemov@...ux.intel.com> wrote:
> > On Mon, Apr 24, 2017 at 09:01:58PM +0300, Kirill A. Shutemov wrote:
> >> On Mon, Apr 24, 2017 at 10:47:43AM -0700, Dan Williams wrote:
> >> I think it's still better to do it on page_ref_* level.
> >
> > Something like patch below? What do you think?
> 
> From a quick glance, I think this looks like the right way to go.

Okay, but I still would like to remove manipulation with pgmap->ref from
hot path.

Can we just check that page_count() match our expectation on
devm_memremap_pages_release() instead of this?

I probably miss something in bigger picture, but would something like
patch work too? It seems work for the test case.

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a835edd2db34..695da2a19b4c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -762,19 +762,11 @@ static inline enum zone_type page_zonenum(const struct page *page)
 }
 
 #ifdef CONFIG_ZONE_DEVICE
-void get_zone_device_page(struct page *page);
-void put_zone_device_page(struct page *page);
 static inline bool is_zone_device_page(const struct page *page)
 {
 	return page_zonenum(page) == ZONE_DEVICE;
 }
 #else
-static inline void get_zone_device_page(struct page *page)
-{
-}
-static inline void put_zone_device_page(struct page *page)
-{
-}
 static inline bool is_zone_device_page(const struct page *page)
 {
 	return false;
@@ -790,9 +782,6 @@ static inline void get_page(struct page *page)
 	 */
 	VM_BUG_ON_PAGE(page_ref_count(page) <= 0, page);
 	page_ref_inc(page);
-
-	if (unlikely(is_zone_device_page(page)))
-		get_zone_device_page(page);
 }
 
 static inline void put_page(struct page *page)
@@ -801,9 +790,6 @@ static inline void put_page(struct page *page)
 
 	if (put_page_testzero(page))
 		__put_page(page);
-
-	if (unlikely(is_zone_device_page(page)))
-		put_zone_device_page(page);
 }
 
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
diff --git a/kernel/memremap.c b/kernel/memremap.c
index 07e85e5229da..e542bb2f7ab0 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -182,18 +182,6 @@ struct page_map {
 	struct vmem_altmap altmap;
 };
 
-void get_zone_device_page(struct page *page)
-{
-	percpu_ref_get(page->pgmap->ref);
-}
-EXPORT_SYMBOL(get_zone_device_page);
-
-void put_zone_device_page(struct page *page)
-{
-	put_dev_pagemap(page->pgmap);
-}
-EXPORT_SYMBOL(put_zone_device_page);
-
 static void pgmap_radix_release(struct resource *res)
 {
 	resource_size_t key, align_start, align_size, align_end;
@@ -237,12 +225,21 @@ static void devm_memremap_pages_release(struct device *dev, void *data)
 	struct resource *res = &page_map->res;
 	resource_size_t align_start, align_size;
 	struct dev_pagemap *pgmap = &page_map->pgmap;
+	unsigned long pfn;
 
 	if (percpu_ref_tryget_live(pgmap->ref)) {
 		dev_WARN(dev, "%s: page mapping is still live!\n", __func__);
 		percpu_ref_put(pgmap->ref);
 	}
 
+	for_each_device_pfn(pfn, page_map) {
+		struct page *page = pfn_to_page(pfn);
+
+		dev_WARN_ONCE(dev, page_count(page) != 1,
+				"%s: unexpected page count: %d!\n",
+				__func__, page_count(page));
+	}
+
 	/* pages are dead and unused, undo the arch mapping */
 	align_start = res->start & ~(SECTION_SIZE - 1);
 	align_size = ALIGN(resource_size(res), SECTION_SIZE);
-- 
 Kirill A. Shutemov