lkml.org 
[lkml]   [2017]   [May]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [HMM 08/15] mm/ZONE_DEVICE: special case put_page() for device private pages
    On Mon, May 22, 2017 at 1:14 PM, Jerome Glisse <jglisse@redhat.com> wrote:
    > On Mon, May 22, 2017 at 12:29:53PM -0700, Dan Williams wrote:
    >> On Mon, May 22, 2017 at 9:51 AM, Jérôme Glisse <jglisse@redhat.com> wrote:
    >> > A ZONE_DEVICE page that reach a refcount of 1 is free ie no longer
    >> > have any user. For device private pages this is important to catch
    >> > and thus we need to special case put_page() for this.
    >> >
    >> > Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
    >> > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    >> > Cc: Dan Williams <dan.j.williams@intel.com>
    >> > Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
    >> > ---
    >> > include/linux/mm.h | 30 ++++++++++++++++++++++++++++++
    >> > kernel/memremap.c | 1 -
    >> > 2 files changed, 30 insertions(+), 1 deletion(-)
    >> >
    >> > diff --git a/include/linux/mm.h b/include/linux/mm.h
    >> > index a825dab..11f7bac 100644
    >> > --- a/include/linux/mm.h
    >> > +++ b/include/linux/mm.h
    >> > @@ -23,6 +23,7 @@
    >> > #include <linux/page_ext.h>
    >> > #include <linux/err.h>
    >> > #include <linux/page_ref.h>
    >> > +#include <linux/memremap.h>
    >> >
    >> > struct mempolicy;
    >> > struct anon_vma;
    >> > @@ -795,6 +796,20 @@ static inline bool is_device_private_page(const struct page *page)
    >> > return ((page_zonenum(page) == ZONE_DEVICE) &&
    >> > (page->pgmap->type == MEMORY_DEVICE_PRIVATE));
    >> > }
    >> > +
    >> > +static inline void put_zone_device_private_page(struct page *page)
    >> > +{
    >> > + int count = page_ref_dec_return(page);
    >> > +
    >> > + /*
    >> > + * If refcount is 1 then page is freed and refcount is stable as nobody
    >> > + * holds a reference on the page.
    >> > + */
    >> > + if (count == 1)
    >> > + page->pgmap->page_free(page, page->pgmap->data);
    >> > + else if (!count)
    >> > + __put_page(page);
    >> > +}
    >> > #else
    >> > static inline bool is_zone_device_page(const struct page *page)
    >> > {
    >> > @@ -805,6 +820,10 @@ static inline bool is_device_private_page(const struct page *page)
    >> > {
    >> > return false;
    >> > }
    >> > +
    >> > +static inline void put_zone_device_private_page(struct page *page)
    >> > +{
    >> > +}
    >> > #endif
    >> >
    >> > static inline void get_page(struct page *page)
    >> > @@ -822,6 +841,17 @@ static inline void put_page(struct page *page)
    >> > {
    >> > page = compound_head(page);
    >> >
    >> > + /*
    >> > + * For private device pages we need to catch refcount transition from
    >> > + * 2 to 1, when refcount reach one it means the private device page is
    >> > + * free and we need to inform the device driver through callback. See
    >> > + * include/linux/memremap.h and HMM for details.
    >> > + */
    >> > + if (unlikely(is_device_private_page(page))) {
    >>
    >> Since I presume HMM is a niche use case can we make this a
    >> "static_branch_unlikely(&hmm_key) && is_device_private_page(page))"?
    >> That way non-hmm platforms see minimal overhead.
    >
    > Like i said in the cover letter i am bit anxious about doing for

    I don't think you copied me on the cover letter.

    > an inline function. I don't see any existing case for inline
    > function and static key. Is that suppose to work ?
    >
    > How widespread HMM use will be is hard to guess. Usual chicken
    > and egg plus adoption thing. If GPGPU compte keeps growing and
    > it seems it does then HMM likely gonna be enable and actively
    > use for large chunk of those computer that have GPGPU workload.
    >
    > I will test a static key of that branch and see if it explodes
    > because put_page() is an inline function.

    memcpy_mcsafe() is an existing example of a static inline with a
    static branch. Hasn't seemed to have caused any problems to date.

    \
     
     \ /
      Last update: 2017-05-22 22:19    [W:4.139 / U:0.152 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site