| Message ID | 20200201034029.4063170-5-jhubbard@nvidia.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/gup: track FOLL_PIN pages | expand |
On Fri, Jan 31, 2020 at 07:40:21PM -0800, John Hubbard wrote: > An upcoming patch requires subtracting a large chunk of refcounts from > a page, and checking what the resulting refcount is. This is a little > different than the usual "check for zero refcount" that many of the > page ref functions already do. However, it is similar to a few other > routines that (like this one) are generally useful for things such as > 1-based refcounting. > > Add page_ref_sub_return(), that subtracts a chunk of refcounts > atomically, and returns an atomic snapshot of the result. > > Signed-off-by: John Hubbard <jhubbard@nvidia.com> > --- > include/linux/page_ref.h | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h > index 14d14beb1f7f..b9cbe553d1e7 100644 > --- a/include/linux/page_ref.h > +++ b/include/linux/page_ref.h > @@ -102,6 +102,16 @@ static inline void page_ref_sub(struct page *page, int nr) > __page_ref_mod(page, -nr); > } > > +static inline int page_ref_sub_return(struct page *page, int nr) > +{ > + int ret = atomic_sub_return(nr, &page->_refcount); > + > + if (page_ref_tracepoint_active(__tracepoint_page_ref_mod)) > + __page_ref_mod(page, -nr); Shouldn't it be __page_ref_mod_and_return() and relevant tracepoint? > + > + return ret; > +} > + > static inline void page_ref_inc(struct page *page) > { > atomic_inc(&page->_refcount); > -- > 2.25.0 >
On 2/3/20 5:23 AM, Kirill A. Shutemov wrote: > On Fri, Jan 31, 2020 at 07:40:21PM -0800, John Hubbard wrote: >> An upcoming patch requires subtracting a large chunk of refcounts from >> a page, and checking what the resulting refcount is. This is a little >> different than the usual "check for zero refcount" that many of the >> page ref functions already do. However, it is similar to a few other >> routines that (like this one) are generally useful for things such as >> 1-based refcounting. >> >> Add page_ref_sub_return(), that subtracts a chunk of refcounts >> atomically, and returns an atomic snapshot of the result. >> >> Signed-off-by: John Hubbard <jhubbard@nvidia.com> >> --- >> include/linux/page_ref.h | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h >> index 14d14beb1f7f..b9cbe553d1e7 100644 >> --- a/include/linux/page_ref.h >> +++ b/include/linux/page_ref.h >> @@ -102,6 +102,16 @@ static inline void page_ref_sub(struct page *page, int nr) >> __page_ref_mod(page, -nr); >> } >> >> +static inline int page_ref_sub_return(struct page *page, int nr) >> +{ >> + int ret = atomic_sub_return(nr, &page->_refcount); >> + >> + if (page_ref_tracepoint_active(__tracepoint_page_ref_mod)) >> + __page_ref_mod(page, -nr); > > Shouldn't it be __page_ref_mod_and_return() and relevant tracepoint? Why yes, it should. I didn't even notice that that more precise function existed, thanks for catching that. I've changed it to this for the next version of the patchset: static inline int page_ref_sub_return(struct page *page, int nr) { int ret = atomic_sub_return(nr, &page->_refcount); if (page_ref_tracepoint_active(__tracepoint_page_ref_mod)) __page_ref_mod_and_return(page, -nr, ret); return ret; } thanks,
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h index 14d14beb1f7f..b9cbe553d1e7 100644 --- a/include/linux/page_ref.h +++ b/include/linux/page_ref.h @@ -102,6 +102,16 @@ static inline void page_ref_sub(struct page *page, int nr) __page_ref_mod(page, -nr); } +static inline int page_ref_sub_return(struct page *page, int nr) +{ + int ret = atomic_sub_return(nr, &page->_refcount); + + if (page_ref_tracepoint_active(__tracepoint_page_ref_mod)) + __page_ref_mod(page, -nr); + + return ret; +} + static inline void page_ref_inc(struct page *page) { atomic_inc(&page->_refcount);
An upcoming patch requires subtracting a large chunk of refcounts from a page, and checking what the resulting refcount is. This is a little different than the usual "check for zero refcount" that many of the page ref functions already do. However, it is similar to a few other routines that (like this one) are generally useful for things such as 1-based refcounting. Add page_ref_sub_return(), that subtracts a chunk of refcounts atomically, and returns an atomic snapshot of the result. Signed-off-by: John Hubbard <jhubbard@nvidia.com> --- include/linux/page_ref.h | 10 ++++++++++ 1 file changed, 10 insertions(+)