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fsdax: set a CoW flag when associate reflink mappings 

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.

Link: https://lkml.kernel.org/r/20220603053738.1218681-8-ruansy.fnst@fujitsu.com
Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dan Williams <dan.j.wiliams@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Goldwyn Rodrigues <rgoldwyn@suse.com>
Cc: Goldwyn Rodrigues <rgoldwyn@suse.de>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Shiyang Ruan 2022-06-03 13:37:31 +08:00 committed by akpm
parent 6f643c57d5
commit 6061b69b9a
2 changed files with 47 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

50
fs/dax.c
View File

@ -334,13 +334,35 @@ static unsigned long dax_end_pfn(void *entry)
for (pfn = dax_to_pfn(entry); \
pfn < dax_end_pfn(entry); pfn++)
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 the page->mapping with FS_DAX_MAPPING_COW flag, increase the refcount.
*/
static inline void dax_mapping_set_cow(struct page *page)
{
if ((uintptr_t)page->mapping != PAGE_MAPPING_DAX_COW) {
/*
* Reset the index if the page was already mapped
* regularly before.
*/
if (page->mapping)
page->index = 1;
page->mapping = (void *)PAGE_MAPPING_DAX_COW;
}
page->index++;
}
/*
* 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
* 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 +374,13 @@ 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) {
dax_mapping_set_cow(page);
} else {
WARN_ON_ONCE(page->mapping);
page->mapping = mapping;
page->index = index + i++;
}
}
}
@ -370,7 +396,12 @@ 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;
}
@ -830,7 +861,8 @@ 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

6
include/linux/page-flags.h
View File

@ -661,6 +661,12 @@ PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted)
#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 bool folio_mapping_flags(struct folio *folio)
{
return ((unsigned long)folio->mapping & PAGE_MAPPING_FLAGS) != 0;