| Message ID | 20200829080853.20337-2-jhubbard@nvidia.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | bio: Direct IO: convert to pin_user_pages_fast() | expand |
On Sat, Aug 29, 2020 at 01:08:51AM -0700, John Hubbard wrote: > pin_user_page() is the FOLL_PIN equivalent of get_page(). > > This was always a missing piece of the pin/unpin API calls (early > reviewers of pin_user_pages() asked about it, in fact), but until now, > it just wasn't needed. Finally though, now that the Direct IO pieces in > block/bio are about to be converted to use FOLL_PIN, it turns out that > there are some cases in which get_page() and get_user_pages_fast() were > both used. Converting those sites requires a drop-in replacement for > get_page(), which this patch supplies. I find the name really confusing vs pin_user_pages*, as it suggests as single version of the same. It also seems partially wrong, at least in the direct I/O case as the only thing pinned here is the zero page. So maybe pin_kernel_page is a better name together with an explanation? Or just pin_page?
On 8/29/20 7:54 AM, Christoph Hellwig wrote: > On Sat, Aug 29, 2020 at 01:08:51AM -0700, John Hubbard wrote: >> pin_user_page() is the FOLL_PIN equivalent of get_page(). >> >> This was always a missing piece of the pin/unpin API calls (early >> reviewers of pin_user_pages() asked about it, in fact), but until now, >> it just wasn't needed. Finally though, now that the Direct IO pieces in >> block/bio are about to be converted to use FOLL_PIN, it turns out that >> there are some cases in which get_page() and get_user_pages_fast() were >> both used. Converting those sites requires a drop-in replacement for >> get_page(), which this patch supplies. > > I find the name really confusing vs pin_user_pages*, as it suggests as > single version of the same. It also seems partially wrong, at least > in the direct I/O case as the only thing pinned here is the zero page. > > So maybe pin_kernel_page is a better name together with an explanation? > Or just pin_page? > Yes. Both its behavior and use are closer to get_page() than it is to get_user_pages(). So pin_page() is just right. thanks,
diff --git a/include/linux/mm.h b/include/linux/mm.h index 97c83773b6f0..51c6ae4b63f7 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1152,6 +1152,8 @@ static inline void get_page(struct page *page) page_ref_inc(page); } +void pin_user_page(struct page *page); + bool __must_check try_grab_page(struct page *page, unsigned int flags); static inline __must_check bool try_get_page(struct page *page) diff --git a/mm/gup.c b/mm/gup.c index ae096ea7583f..2cae5bbbc862 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -123,6 +123,36 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page, return NULL; } +/* + * pin_user_page() - elevate the page refcount, and mark as FOLL_PIN + * + * This the FOLL_PIN equivalent of get_page(). It is intended for use when the + * page will be released via unpin_user_page(). + */ +void pin_user_page(struct page *page) +{ + int refs = 1; + + page = compound_head(page); + + VM_BUG_ON_PAGE(page_ref_count(page) <= 0, page); + + if (hpage_pincount_available(page)) + hpage_pincount_add(page, 1); + else + refs = GUP_PIN_COUNTING_BIAS; + + /* + * Similar to try_grab_compound_head(): even if using the + * hpage_pincount_add/_sub() routines, be sure to + * *also* increment the normal page refcount field at least + * once, so that the page really is pinned. + */ + page_ref_add(page, refs); + + mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1); +} + /** * try_grab_page() - elevate a page's refcount by a flag-dependent amount *
pin_user_page() is the FOLL_PIN equivalent of get_page(). This was always a missing piece of the pin/unpin API calls (early reviewers of pin_user_pages() asked about it, in fact), but until now, it just wasn't needed. Finally though, now that the Direct IO pieces in block/bio are about to be converted to use FOLL_PIN, it turns out that there are some cases in which get_page() and get_user_pages_fast() were both used. Converting those sites requires a drop-in replacement for get_page(), which this patch supplies. [1] and [2] provide some background about pin_user_pages() in general. [1] "Explicit pinning of user-space pages": https://lwn.net/Articles/807108/ [2] Documentation/core-api/pin_user_pages.rst Signed-off-by: John Hubbard <jhubbard@nvidia.com> --- include/linux/mm.h | 2 ++ mm/gup.c | 30 ++++++++++++++++++++++++++++++ 2 files changed, 32 insertions(+)