| Message ID | 20201027025523.3235-1-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/page_alloc: Add __free_pages documentation | expand |
I like the explanation. Reviewed-by: William Kucharski <william.kucharski@oracle.com> > On Oct 26, 2020, at 8:55 PM, Matthew Wilcox (Oracle) <willy@infradead.org> wrote: > > Provide some guidance towards when this might not be the right interface > to use. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > --- > mm/page_alloc.c | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 23f5066bd4a5..e613177b8041 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5007,6 +5007,26 @@ static inline void free_the_page(struct page *page, unsigned int order) > __free_pages_ok(page, order, FPI_NONE); > } > > +/** > + * __free_pages - Free pages allocated with alloc_pages(). > + * @page: The page pointer returned from alloc_pages(). > + * @order: The order of the allocation. > + * > + * This function can free multi-page allocations that are not compound > + * pages. It does not check that the @order passed in matches that of > + * the allocation, so it is easy to leak memory. Freeing more memory > + * than was allocated will probably emit a warning. > + * > + * If the last reference to this page is speculative, it will be released > + * by put_page() which only frees the first page of a non-compound > + * allocation. To prevent the remaining pages from being leaked, we free > + * the subsequent pages here. If you want to use the page's reference > + * count to decide when to free the allocation, you should allocate a > + * compound page, and use put_page() instead of __free_pages(). > + * > + * Context: May be called in interrupt context or while holding a normal > + * spinlock, but not in NMI context or while holding a raw spinlock. > + */ > void __free_pages(struct page *page, unsigned int order) > { > if (put_page_testzero(page)) > -- > 2.28.0 > >
On 10/27/20 3:55 AM, Matthew Wilcox (Oracle) wrote: > Provide some guidance towards when this might not be the right interface > to use. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Acked-by: Vlastimil Babka <vbabka@suse.cz> > --- > mm/page_alloc.c | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 23f5066bd4a5..e613177b8041 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5007,6 +5007,26 @@ static inline void free_the_page(struct page *page, unsigned int order) > __free_pages_ok(page, order, FPI_NONE); > } > > +/** > + * __free_pages - Free pages allocated with alloc_pages(). > + * @page: The page pointer returned from alloc_pages(). > + * @order: The order of the allocation. > + * > + * This function can free multi-page allocations that are not compound > + * pages. It does not check that the @order passed in matches that of > + * the allocation, so it is easy to leak memory. Freeing more memory > + * than was allocated will probably emit a warning. > + * > + * If the last reference to this page is speculative, it will be released > + * by put_page() which only frees the first page of a non-compound > + * allocation. To prevent the remaining pages from being leaked, we free > + * the subsequent pages here. If you want to use the page's reference > + * count to decide when to free the allocation, you should allocate a > + * compound page, and use put_page() instead of __free_pages(). > + * > + * Context: May be called in interrupt context or while holding a normal > + * spinlock, but not in NMI context or while holding a raw spinlock. > + */ > void __free_pages(struct page *page, unsigned int order) > { > if (put_page_testzero(page)) >
On Tue, Oct 27, 2020 at 02:55:23AM +0000, Matthew Wilcox (Oracle) wrote: > Provide some guidance towards when this might not be the right interface > to use. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> > --- > mm/page_alloc.c | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 23f5066bd4a5..e613177b8041 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5007,6 +5007,26 @@ static inline void free_the_page(struct page *page, unsigned int order) > __free_pages_ok(page, order, FPI_NONE); > } > > +/** > + * __free_pages - Free pages allocated with alloc_pages(). > + * @page: The page pointer returned from alloc_pages(). > + * @order: The order of the allocation. > + * > + * This function can free multi-page allocations that are not compound > + * pages. It does not check that the @order passed in matches that of > + * the allocation, so it is easy to leak memory. Freeing more memory > + * than was allocated will probably emit a warning. > + * > + * If the last reference to this page is speculative, it will be released > + * by put_page() which only frees the first page of a non-compound > + * allocation. To prevent the remaining pages from being leaked, we free > + * the subsequent pages here. If you want to use the page's reference > + * count to decide when to free the allocation, you should allocate a > + * compound page, and use put_page() instead of __free_pages(). > + * > + * Context: May be called in interrupt context or while holding a normal > + * spinlock, but not in NMI context or while holding a raw spinlock. > + */ > void __free_pages(struct page *page, unsigned int order) > { > if (put_page_testzero(page)) > -- > 2.28.0 > >
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 23f5066bd4a5..e613177b8041 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5007,6 +5007,26 @@ static inline void free_the_page(struct page *page, unsigned int order) __free_pages_ok(page, order, FPI_NONE); } +/** + * __free_pages - Free pages allocated with alloc_pages(). + * @page: The page pointer returned from alloc_pages(). + * @order: The order of the allocation. + * + * This function can free multi-page allocations that are not compound + * pages. It does not check that the @order passed in matches that of + * the allocation, so it is easy to leak memory. Freeing more memory + * than was allocated will probably emit a warning. + * + * If the last reference to this page is speculative, it will be released + * by put_page() which only frees the first page of a non-compound + * allocation. To prevent the remaining pages from being leaked, we free + * the subsequent pages here. If you want to use the page's reference + * count to decide when to free the allocation, you should allocate a + * compound page, and use put_page() instead of __free_pages(). + * + * Context: May be called in interrupt context or while holding a normal + * spinlock, but not in NMI context or while holding a raw spinlock. + */ void __free_pages(struct page *page, unsigned int order) { if (put_page_testzero(page))
Provide some guidance towards when this might not be the right interface to use. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- mm/page_alloc.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)