Re: [PATCH 2/2] mm: remove extra ZONE_DEVICE struct page refcount
From: Ralph Campbell
Date: Mon Sep 28 2020 - 19:40:58 EST
On 9/25/20 11:41 PM, Christoph Hellwig wrote:
On Fri, Sep 25, 2020 at 01:44:42PM -0700, Ralph Campbell wrote:
ZONE_DEVICE struct pages have an extra reference count that complicates the
code for put_page() and several places in the kernel that need to check the
reference count to see that a page is not being used (gup, compaction,
migration, etc.). Clean up the code so the reference count doesn't need to
be treated specially for ZONE_DEVICE.
Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
---
arch/powerpc/kvm/book3s_hv_uvmem.c | 2 +-
drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +-
include/linux/dax.h | 2 +-
include/linux/memremap.h | 7 ++-
include/linux/mm.h | 44 --------------
lib/test_hmm.c | 2 +-
mm/gup.c | 44 --------------
mm/internal.h | 8 +++
mm/memremap.c | 82 ++++++--------------------
mm/migrate.c | 5 --
mm/page_alloc.c | 3 +
mm/swap.c | 46 +++------------
12 files changed, 44 insertions(+), 203 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index 7705d5557239..e6ec98325fab 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -711,7 +711,7 @@ static struct page *kvmppc_uvmem_get_page(unsigned long gpa, struct kvm *kvm)
dpage = pfn_to_page(uvmem_pfn);
dpage->zone_device_data = pvt;
- get_page(dpage);
+ init_page_count(dpage);
lock_page(dpage);
return dpage;
out_clear:
diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 4e8112fde3e6..ca2e3c3edc36 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -323,7 +323,7 @@ nouveau_dmem_page_alloc_locked(struct nouveau_drm *drm)
return NULL;
}
- get_page(page);
+ init_page_count(page);
lock_page(page);
return page;
}
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 3f78ed78d1d6..8d29f38645aa 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -240,7 +240,7 @@ static inline bool dax_mapping(struct address_space *mapping)
static inline bool dax_layout_is_idle_page(struct page *page)
{
- return page_ref_count(page) <= 1;
+ return page_ref_count(page) == 0;
}
#endif
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index e5862746751b..f9224f88e4cd 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -65,9 +65,10 @@ enum memory_type {
struct dev_pagemap_ops {
/*
- * Called once the page refcount reaches 1. (ZONE_DEVICE pages never
- * reach 0 refcount unless there is a refcount bug. This allows the
- * device driver to implement its own memory management.)
+ * Called once the page refcount reaches 0. The reference count
+ * should be reset to one with init_page_count(page) before reusing
+ * the page. This allows the device driver to implement its own
+ * memory management.
*/
void (*page_free)(struct page *page);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b2f370f0b420..2159c2477aa3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1092,39 +1092,6 @@ static inline bool is_zone_device_page(const struct page *page)
}
#endif
-#ifdef CONFIG_DEV_PAGEMAP_OPS
-void free_devmap_managed_page(struct page *page);
-DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
-
-static inline bool page_is_devmap_managed(struct page *page)
-{
- if (!static_branch_unlikely(&devmap_managed_key))
- return false;
- if (!is_zone_device_page(page))
- return false;
- switch (page->pgmap->type) {
- case MEMORY_DEVICE_PRIVATE:
- case MEMORY_DEVICE_FS_DAX:
- return true;
- default:
- break;
- }
- return false;
-}
-
-void put_devmap_managed_page(struct page *page);
-
-#else /* CONFIG_DEV_PAGEMAP_OPS */
-static inline bool page_is_devmap_managed(struct page *page)
-{
- return false;
-}
-
-static inline void put_devmap_managed_page(struct page *page)
-{
-}
-#endif /* CONFIG_DEV_PAGEMAP_OPS */
-
static inline bool is_device_private_page(const struct page *page)
{
return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) &&
@@ -1171,17 +1138,6 @@ static inline void put_page(struct page *page)
{
page = compound_head(page);
- /*
- * For devmap managed pages we need to catch refcount transition from
- * 2 to 1, when refcount reach one it means the page is free and we
- * need to inform the device driver through callback. See
- * include/linux/memremap.h and HMM for details.
- */
- if (page_is_devmap_managed(page)) {
- put_devmap_managed_page(page);
- return;
- }
-
if (put_page_testzero(page))
__put_page(page);
}
diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index e7dc3de355b7..1033b19c9c52 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -561,7 +561,7 @@ static struct page *dmirror_devmem_alloc_page(struct dmirror_device *mdevice)
}
dpage->zone_device_data = rpage;
- get_page(dpage);
+ init_page_count(dpage);
lock_page(dpage);
return dpage;
Doesn't test_hmm also need to reinitialize the refcount before freeing
the page in hmm_dmirror_exit?
The dmirror_zero_page is dead code, it isn't used. There is a patch queued in
linux-mm which removes it. Besides, it was allocated with alloc_page() so it
isn't a device private struct page.
int error, is_ram;
- bool need_devmap_managed = true;
switch (pgmap->type) {
case MEMORY_DEVICE_PRIVATE:
@@ -217,11 +171,9 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
}
break;
case MEMORY_DEVICE_GENERIC:
The MEMORY_DEVICE_PRIVATE cases loses the sanity check that the
page_free method is set.
I'll add that back into memremap_pages() with other sanity checks in v3.
Otherwise this looks good.
Thanks!