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mm: extend prefault helpers to fault in more than PAGE_SIZE

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drm/i915 wants to read/write more than one page in its fastpath
and hence needs to prefault more than PAGE_SIZE bytes.

Add new functions in filemap.h to make that possible.

Also kill a copy&pasted spurious space in both functions while at it.

v2: As suggested by Andrew Morton, add a multipage parameter to both
functions to avoid the additional branch for the pagemap.c hotpath.
My gcc 4.6 here seems to dtrt and indeed reap these branches where not
needed.

v3: Becaus I couldn't find a way around adding a uaddr += PAGE_SIZE to
the filemap.c hotpaths (that the compiler couldn't remove again),
let's go with separate new functions for the multipage use-case.

v4: Adjust comment to CodingStlye and fix spelling.

Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Daniel Vetter 2012-03-25 19:47:41 +02:00
parent d174bd6472
commit f56f821feb
3 changed files with 66 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

64
include/linux/pagemap.h
View file

@ -426,7 +426,7 @@ static inline int fault_in_pages_writeable(char __user *uaddr, int size)
*/
if (((unsigned long)uaddr & PAGE_MASK) !=
((unsigned long)end & PAGE_MASK))
ret = __put_user(0, end);
ret = __put_user(0, end);
}
return ret;
}
@ -445,13 +445,73 @@ static inline int fault_in_pages_readable(const char __user *uaddr, int size)
if (((unsigned long)uaddr & PAGE_MASK) !=
((unsigned long)end & PAGE_MASK)) {
ret = __get_user(c, end);
ret = __get_user(c, end);
(void)c;
}
}
return ret;
}
/*
* Multipage variants of the above prefault helpers, useful if more than
* PAGE_SIZE of data needs to be prefaulted. These are separate from the above
* functions (which only handle up to PAGE_SIZE) to avoid clobbering the
* filemap.c hotpaths.
*/
static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
{
int ret;
const char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return 0;
/*
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
*/
while (uaddr <= end) {
ret = __put_user(0, uaddr);
if (ret != 0)
return ret;
uaddr += PAGE_SIZE;
}
/* Check whether the range spilled into the next page. */
if (((unsigned long)uaddr & PAGE_MASK) ==
((unsigned long)end & PAGE_MASK))
ret = __put_user(0, end);
return ret;
}
static inline int fault_in_multipages_readable(const char __user *uaddr,
int size)
{
volatile char c;
int ret;
const char __user *end = uaddr + size - 1;
if (unlikely(size == 0))
return 0;
while (uaddr <= end) {
ret = __get_user(c, uaddr);
if (ret != 0)
return ret;
uaddr += PAGE_SIZE;
}
/* Check whether the range spilled into the next page. */
if (((unsigned long)uaddr & PAGE_MASK) ==
((unsigned long)end & PAGE_MASK)) {
ret = __get_user(c, end);
(void)c;
}
return ret;
}
int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
pgoff_t index, gfp_t gfp_mask);
int add_to_page_cache_lru(struct page *page, struct address_space *mapping,