On 10/26/21 10:53, John Hubbard wrote:
On 10/26/21 10:38, Pasha Tatashin wrote:set_page_refcounted() converts a non-refcounted page that has (page->_refcount == 0) into a refcounted page by setting _refcount to 1, Use page_ref_inc_return() instead to avoid unconditionally overwriting the _refcount value. Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> --- mm/internal.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/internal.h b/mm/internal.h index cf3cb933eba3..cf345fac6894 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -91,9 +91,12 @@ static inline bool page_evictable(struct page *page) */ static inline void set_page_refcounted(struct page *page) { + int refcnt; + VM_BUG_ON_PAGE(PageTail(page), page); VM_BUG_ON_PAGE(page_ref_count(page), page); - set_page_count(page, 1); + refcnt = page_ref_inc_return(page); + VM_BUG_ON_PAGE(refcnt != 1, page);Hi Pavel,
ohhh, s/Pavel/Pasha/ ! Huge apologies for the name mixup, I had just seen another email... very sorry about that mistake. thanks, -- John Hubbard NVIDIA
I am acutely uncomfortable with this change, because it changes the meaning and behavior of the function to something completely different, while leaving the function name unchanged. Furthermore, in relies upon debug assertions, rather than a return value (for example) to verify that all is well. I understand where this patchset is going, but this intermediate step is not a good move. Also, for the overall series, if you want to change from "set_page_count()" to "inc_and_verify_val_equals_one()", then the way to do that is *not* to depend solely on VM_BUG*() to verify. Instead, return something like -EBUSY if incrementing the value results in a surprise, and let the caller decide how to handle it. thanks,
