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Subject[PATCH v10 03/25] mm: Cleanup __put_devmap_managed_page() vs ->page_free()
Date
From: Dan Williams <dan.j.williams@intel.com>

After the removal of the device-public infrastructure there are only 2
->page_free() call backs in the kernel. One of those is a device-private
callback in the nouveau driver, the other is a generic wakeup needed in
the DAX case. In the hopes that all ->page_free() callbacks can be
migrated to common core kernel functionality, move the device-private
specific actions in __put_devmap_managed_page() under the
is_device_private_page() conditional, including the ->page_free()
callback. For the other page types just open-code the generic wakeup.

Yes, the wakeup is only needed in the MEMORY_DEVICE_FSDAX case, but it
does no harm in the MEMORY_DEVICE_DEVDAX and MEMORY_DEVICE_PCI_P2PDMA
case.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
drivers/nvdimm/pmem.c | 6 ----
mm/memremap.c | 80 ++++++++++++++++++++++++-------------------
2 files changed, 44 insertions(+), 42 deletions(-)

diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index ad8e4df1282b..4eae441f86c9 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -337,13 +337,7 @@ static void pmem_release_disk(void *__pmem)
put_disk(pmem->disk);
}

-static void pmem_pagemap_page_free(struct page *page)
-{
- wake_up_var(&page->_refcount);
-}
-
static const struct dev_pagemap_ops fsdax_pagemap_ops = {
- .page_free = pmem_pagemap_page_free,
.kill = pmem_pagemap_kill,
.cleanup = pmem_pagemap_cleanup,
};
diff --git a/mm/memremap.c b/mm/memremap.c
index 03ccbdfeb697..e899fa876a62 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -27,7 +27,8 @@ static void devmap_managed_enable_put(void)

static int devmap_managed_enable_get(struct dev_pagemap *pgmap)
{
- if (!pgmap->ops || !pgmap->ops->page_free) {
+ if (pgmap->type == MEMORY_DEVICE_PRIVATE &&
+ (!pgmap->ops || !pgmap->ops->page_free)) {
WARN(1, "Missing page_free method\n");
return -EINVAL;
}
@@ -414,44 +415,51 @@ void __put_devmap_managed_page(struct page *page)
{
int count = page_ref_dec_return(page);

- /*
- * If refcount is 1 then page is freed and refcount is stable as nobody
- * holds a reference on the page.
- */
- if (count == 1) {
- /* Clear Active bit in case of parallel mark_page_accessed */
- __ClearPageActive(page);
- __ClearPageWaiters(page);
+ /* still busy */
+ if (count > 1)
+ return;

- mem_cgroup_uncharge(page);
+ /* only triggered by the dev_pagemap shutdown path */
+ if (count == 0) {
+ __put_page(page);
+ return;
+ }

- /*
- * When a device_private page is freed, the page->mapping field
- * may still contain a (stale) mapping value. For example, the
- * lower bits of page->mapping may still identify the page as
- * an anonymous page. Ultimately, this entire field is just
- * stale and wrong, and it will cause errors if not cleared.
- * One example is:
- *
- * migrate_vma_pages()
- * migrate_vma_insert_page()
- * page_add_new_anon_rmap()
- * __page_set_anon_rmap()
- * ...checks page->mapping, via PageAnon(page) call,
- * and incorrectly concludes that the page is an
- * anonymous page. Therefore, it incorrectly,
- * silently fails to set up the new anon rmap.
- *
- * For other types of ZONE_DEVICE pages, migration is either
- * handled differently or not done at all, so there is no need
- * to clear page->mapping.
- */
- if (is_device_private_page(page))
- page->mapping = NULL;
+ /* notify page idle for dax */
+ if (!is_device_private_page(page)) {
+ wake_up_var(&page->_refcount);
+ return;
+ }

- page->pgmap->ops->page_free(page);
- } else if (!count)
- __put_page(page);
+ /* Clear Active bit in case of parallel mark_page_accessed */
+ __ClearPageActive(page);
+ __ClearPageWaiters(page);
+
+ mem_cgroup_uncharge(page);
+
+ /*
+ * When a device_private page is freed, the page->mapping field
+ * may still contain a (stale) mapping value. For example, the
+ * lower bits of page->mapping may still identify the page as an
+ * anonymous page. Ultimately, this entire field is just stale
+ * and wrong, and it will cause errors if not cleared. One
+ * example is:
+ *
+ * migrate_vma_pages()
+ * migrate_vma_insert_page()
+ * page_add_new_anon_rmap()
+ * __page_set_anon_rmap()
+ * ...checks page->mapping, via PageAnon(page) call,
+ * and incorrectly concludes that the page is an
+ * anonymous page. Therefore, it incorrectly,
+ * silently fails to set up the new anon rmap.
+ *
+ * For other types of ZONE_DEVICE pages, migration is either
+ * handled differently or not done at all, so there is no need
+ * to clear page->mapping.
+ */
+ page->mapping = NULL;
+ page->pgmap->ops->page_free(page);
}
EXPORT_SYMBOL(__put_devmap_managed_page);
#endif /* CONFIG_DEV_PAGEMAP_OPS */
--
2.24.0
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