On 2024/9/26 21:40, Matthew Wilcox wrote:
On Thu, Sep 26, 2024 at 02:58:31PM +0200, Daniel Gomez wrote:
On 9/26/2024 2:16 PM, Matthew Wilcox wrote:
On Thu, Sep 26, 2024 at 04:27:26PM +0800, Baolin Wang wrote:
+static inline unsigned int
+shmem_mapping_size_order(struct address_space *mapping, pgoff_t index, size_t size)
+{
+ unsigned int order = get_order(max_t(size_t, size, PAGE_SIZE));
Why introduce the max_t() call here? Did nobody read the documentation
or implementation for get_order() before writing this patch?
get_order() result is undefined if the size is 0. I've used max_t() here to
avoid that case. Perhaps should we prevent that case before getting here?
Surely we've handled a length-0 write before we get here?
I think one of my earlier attemps was to use fgf_set_order + FGF_GET_ORDER()
as in iomap. But the solution taken there was to share code between shmem
and filemap and that wasn't considered a good idea. Shall we just replicate
iomap_get_folio()? Or else, what do you suggest here?
We could move three of the four lines from fgf_set_order() into a
new function and call it from both fgf_set_order() and shmem?
Sounds good. How about the following changes? Do you have a perferred
name for the new helper? Thanks.
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index d9c7edb6422b..ce418acd2737 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -629,6 +629,16 @@ typedef unsigned int __bitwise fgf_t;
#define FGP_WRITEBEGIN (FGP_LOCK | FGP_WRITE | FGP_CREAT |
FGP_STABLE)
+static inline unsigned int filemap_get_order(size_t size)
+{
+ unsigned int shift = ilog2(size);
+
+ if (shift <= PAGE_SHIFT)
+ return 0;
+
+ return shift - PAGE_SHIFT;
+}
+
/**
* fgf_set_order - Encode a length in the fgf_t flags.
* @size: The suggested size of the folio to create.
@@ -642,11 +652,11 @@ typedef unsigned int __bitwise fgf_t;
*/
static inline fgf_t fgf_set_order(size_t size)
{
- unsigned int shift = ilog2(size);
+ unsigned int order = filemap_get_order(size);
- if (shift <= PAGE_SHIFT)
+ if (!order)
return 0;
- return (__force fgf_t)((shift - PAGE_SHIFT) << 26);
+ return (__force fgf_t)(order << 26);
}
void *filemap_get_entry(struct address_space *mapping, pgoff_t index);
