From: Shiyang Ruan <ruansy.fnst@fujitsu.com>
To: <linux-kernel@vger.kernel.org>, <linux-xfs@vger.kernel.org>,
<nvdimm@lists.linux.dev>, <linux-mm@kvack.org>,
<linux-fsdevel@vger.kernel.org>
Cc: <djwong@kernel.org>, <dan.j.williams@intel.com>,
<david@fromorbit.com>, <hch@infradead.org>, <jane.chu@oracle.com>
Subject: [PATCH v12 7/7] fsdax: set a CoW flag when associate reflink mappings
Date: Mon, 11 Apr 2022 00:09:04 +0800 [thread overview]
Message-ID: <20220410160904.3758789-8-ruansy.fnst@fujitsu.com> (raw)
In-Reply-To: <20220410160904.3758789-1-ruansy.fnst@fujitsu.com>
Introduce a PAGE_MAPPING_DAX_COW flag to support association with CoW file
mappings. In this case, since the dax-rmap has already took the
responsibility to look up for shared files by given dax page,
the page->mapping is no longer to used for rmap but for marking that
this dax page is shared. And to make sure disassociation works fine, we
use page->index as refcount, and clear page->mapping to the initial
state when page->index is decreased to 0.
With the help of this new flag, it is able to distinguish normal case
and CoW case, and keep the warning in normal case.
==
PS: The @cow added for dax_associate_entry(), is used to let it know
whether the entry is to be shared during iomap operation. It is decided
by iomap,srcmap's flag, and will be used in another patchset(
fsdax,xfs: Add reflink&dedupe support for fsdax[1]).
In this patch, we set @cow always false for now.
[1] https://lore.kernel.org/linux-xfs/20210928062311.4012070-1-ruansy.fnst@fujitsu.com/
==
Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
---
fs/dax.c | 65 ++++++++++++++++++++++++++++++++------
include/linux/page-flags.h | 6 ++++
2 files changed, 62 insertions(+), 9 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index 57efd3f73655..2c2958425b95 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -334,13 +334,46 @@ static unsigned long dax_end_pfn(void *entry)
for (pfn = dax_to_pfn(entry); \
pfn < dax_end_pfn(entry); pfn++)
+static inline void dax_mapping_set_cow_flag(struct address_space **mapping)
+{
+ *mapping = (struct address_space *)PAGE_MAPPING_DAX_COW;
+}
+
+static inline bool dax_mapping_is_cow(struct address_space *mapping)
+{
+ return (unsigned long)mapping == PAGE_MAPPING_DAX_COW;
+}
+
/*
- * TODO: for reflink+dax we need a way to associate a single page with
- * multiple address_space instances at different linear_page_index()
- * offsets.
+ * Set or Update the page->mapping with FS_DAX_MAPPING_COW flag.
+ * Return true if it is an Update.
+ */
+static inline bool dax_mapping_set_cow(struct page *page)
+{
+ if (page->mapping) {
+ /* flag already set */
+ if (dax_mapping_is_cow(page->mapping))
+ return false;
+
+ /*
+ * This page has been mapped even before it is shared, just
+ * need to set this FS_DAX_MAPPING_COW flag.
+ */
+ dax_mapping_set_cow_flag(&page->mapping);
+ return true;
+ }
+ /* Newly associate CoW mapping */
+ dax_mapping_set_cow_flag(&page->mapping);
+ return false;
+}
+
+/*
+ * When it is called in dax_insert_entry(), the cow flag will indicate that
+ * whether this entry is shared by multiple files. If so, set the page->mapping
+ * to be FS_DAX_MAPPING_COW, and use page->index as refcount.
*/
static void dax_associate_entry(void *entry, struct address_space *mapping,
- struct vm_area_struct *vma, unsigned long address)
+ struct vm_area_struct *vma, unsigned long address, bool cow)
{
unsigned long size = dax_entry_size(entry), pfn, index;
int i = 0;
@@ -352,9 +385,17 @@ static void dax_associate_entry(void *entry, struct address_space *mapping,
for_each_mapped_pfn(entry, pfn) {
struct page *page = pfn_to_page(pfn);
- WARN_ON_ONCE(page->mapping);
- page->mapping = mapping;
- page->index = index + i++;
+ if (cow) {
+ if (dax_mapping_set_cow(page)) {
+ /* Was normal, now updated to CoW */
+ page->index = 2;
+ } else
+ page->index++;
+ } else {
+ WARN_ON_ONCE(page->mapping);
+ page->mapping = mapping;
+ page->index = index + i++;
+ }
}
}
@@ -370,7 +411,12 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping,
struct page *page = pfn_to_page(pfn);
WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
- WARN_ON_ONCE(page->mapping && page->mapping != mapping);
+ if (!dax_mapping_is_cow(page->mapping)) {
+ /* keep the CoW flag if this page is still shared */
+ if (page->index-- > 0)
+ continue;
+ } else
+ WARN_ON_ONCE(page->mapping && page->mapping != mapping);
page->mapping = NULL;
page->index = 0;
}
@@ -829,7 +875,8 @@ static void *dax_insert_entry(struct xa_state *xas,
void *old;
dax_disassociate_entry(entry, mapping, false);
- dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address);
+ dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address,
+ false);
/*
* Only swap our new entry into the page cache if the current
* entry is a zero page or an empty entry. If a normal PTE or
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index b70124b9c7c1..e02907150e5c 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -650,6 +650,12 @@ __PAGEFLAG(Reported, reported, PF_NO_COMPOUND)
#define PAGE_MAPPING_KSM (PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE)
#define PAGE_MAPPING_FLAGS (PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE)
+/*
+ * Different with flags above, this flag is used only for fsdax mode. It
+ * indicates that this page->mapping is now under reflink case.
+ */
+#define PAGE_MAPPING_DAX_COW 0x1
+
static __always_inline int PageMappingFlags(struct page *page)
{
return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) != 0;
--
2.35.1
next prev parent reply other threads:[~2022-04-10 16:09 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-10 16:08 [PATCH v12 0/7] fsdax: introduce fs query to support reflink Shiyang Ruan
2022-04-10 16:08 ` [PATCH v12 1/7] dax: Introduce holder for dax_device Shiyang Ruan
2022-04-11 6:35 ` Christoph Hellwig
2022-04-12 23:22 ` Dan Williams
2022-04-10 16:08 ` [PATCH v12 2/7] mm: factor helpers for memory_failure_dev_pagemap Shiyang Ruan
2022-04-10 19:48 ` kernel test robot
2022-04-10 20:19 ` kernel test robot
2022-04-11 6:37 ` Christoph Hellwig
2022-04-11 9:39 ` Shiyang Ruan
2022-04-10 16:09 ` [PATCH v12 3/7] pagemap,pmem: Introduce ->memory_failure() Shiyang Ruan
2022-04-10 16:09 ` [PATCH v12 4/7] fsdax: Introduce dax_lock_mapping_entry() Shiyang Ruan
2022-04-10 16:09 ` [PATCH v12 5/7] mm: Introduce mf_dax_kill_procs() for fsdax case Shiyang Ruan
2022-04-11 6:40 ` wangjianjian (C)
2022-04-11 9:40 ` Shiyang Ruan
2022-04-10 16:09 ` [PATCH v12 6/7] xfs: Implement ->notify_failure() for XFS Shiyang Ruan
2022-04-10 18:58 ` kernel test robot
2022-04-10 23:54 ` kernel test robot
2022-04-11 6:39 ` Christoph Hellwig
2022-04-13 0:04 ` Dave Chinner
2022-04-13 2:06 ` Dan Williams
2022-04-13 6:09 ` Dave Chinner
2022-04-13 17:09 ` Dan Williams
2022-04-13 17:12 ` Christoph Hellwig
2022-04-14 13:22 ` [xfs] bf68be0c39: BUG:KASAN:null-ptr-deref_in_fs_put_dax kernel test robot
2022-04-10 16:09 ` Shiyang Ruan [this message]
2022-04-11 6:55 ` [PATCH v12 7/7] fsdax: set a CoW flag when associate reflink mappings Christoph Hellwig
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