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mm: optimize dev_pagemap reference counting around get_dev_pagemap

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Change the calling convention so that get_dev_pagemap always consumes the
previous reference instead of doing this using an explicit earlier call to
put_dev_pagemap in the callers.

The callers will still need to put the final reference after finishing the
loop over the pages.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Logan Gunthorpe <[email protected]>
Signed-off-by: Dan Williams <[email protected]>
This commit is contained in:
Christoph Hellwig 2017-12-29 08:54:01 +01:00 • committed by Dan Williams
commit 832d7aa051
2 changed files with 14 additions and 10 deletions
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17
kernel/memremap.c
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@ -507,22 +507,23 @@ struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start)
* @pfn: page frame number to lookup page_map
* @pgmap: optional known pgmap that already has a reference
*
* @pgmap allows the overhead of a lookup to be bypassed when @pfn lands in the
* same mapping.
* If @pgmap is non-NULL and covers @pfn it will be returned as-is. If @pgmap
* is non-NULL but does not cover @pfn the reference to it will be released.
*/
struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
struct dev_pagemap *pgmap)
{
const struct resource *res = pgmap ? pgmap->res : NULL;
resource_size_t phys = PFN_PHYS(pfn);
/*
* In the cached case we're already holding a live reference so
* we can simply do a blind increment
* In the cached case we're already holding a live reference.
*/
if (res && phys >= res->start && phys <= res->end) {
percpu_ref_get(pgmap->ref);
return pgmap;
if (pgmap) {
const struct resource *res = pgmap ? pgmap->res : NULL;
if (res && phys >= res->start && phys <= res->end)
return pgmap;
put_dev_pagemap(pgmap);
}
/* fall back to slow path lookup */