| Message ID | 1431622863-28575-11-git-send-email-julien.grall@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 05/14/2015 01:00 PM, Julien Grall wrote: > When Linux is using 64K page granularity, every page will be slipt in > multiple non-contiguous 4K MFN. > > I'm not sure how to handle efficiently the check to know whether we can > merge 2 biovec with a such case. So for now, always says that biovec are > not mergeable. > > Signed-off-by: Julien Grall <julien.grall@citrix.com> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> > Cc: David Vrabel <david.vrabel@citrix.com> > --- > drivers/xen/biomerge.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/xen/biomerge.c b/drivers/xen/biomerge.c > index 0edb91c..20387c2 100644 > --- a/drivers/xen/biomerge.c > +++ b/drivers/xen/biomerge.c > @@ -9,6 +9,9 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1, > unsigned long mfn1 = pfn_to_mfn(page_to_pfn(vec1->bv_page)); > unsigned long mfn2 = pfn_to_mfn(page_to_pfn(vec2->bv_page)); > > + /* TODO: Implement it correctly */ > + return 0; > + > return __BIOVEC_PHYS_MERGEABLE(vec1, vec2) && > ((mfn1 == mfn2) || ((mfn1+1) == mfn2)); > } I think this is a bit too blunt. Perhaps check first whether page sizes are different in the hypervisor and the guest? (And I am not sure we need __BIOVEC_PHYS_MERGEABLE() test here as it is already checked by BIOVEC_PHYS_MERGEABLE() which appears to be the only user of xen_biovec_phys_mergeable()) -boris
Hi Boris, On 15/05/15 16:54, Boris Ostrovsky wrote: > On 05/14/2015 01:00 PM, Julien Grall wrote: >> When Linux is using 64K page granularity, every page will be slipt in >> multiple non-contiguous 4K MFN. >> >> I'm not sure how to handle efficiently the check to know whether we can >> merge 2 biovec with a such case. So for now, always says that biovec are >> not mergeable. >> >> Signed-off-by: Julien Grall <julien.grall@citrix.com> >> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> >> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> >> Cc: David Vrabel <david.vrabel@citrix.com> >> --- >> drivers/xen/biomerge.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/drivers/xen/biomerge.c b/drivers/xen/biomerge.c >> index 0edb91c..20387c2 100644 >> --- a/drivers/xen/biomerge.c >> +++ b/drivers/xen/biomerge.c >> @@ -9,6 +9,9 @@ bool xen_biovec_phys_mergeable(const struct bio_vec >> *vec1, >> unsigned long mfn1 = pfn_to_mfn(page_to_pfn(vec1->bv_page)); >> unsigned long mfn2 = pfn_to_mfn(page_to_pfn(vec2->bv_page)); >> + /* TODO: Implement it correctly */ >> + return 0; >> + >> return __BIOVEC_PHYS_MERGEABLE(vec1, vec2) && >> ((mfn1 == mfn2) || ((mfn1+1) == mfn2)); >> } > > > I think this is a bit too blunt. Perhaps check first whether page sizes > are different in the hypervisor and the guest? Sounds good. > > (And I am not sure we need __BIOVEC_PHYS_MERGEABLE() test here as it is > already checked by BIOVEC_PHYS_MERGEABLE() which appears to be the only > user of xen_biovec_phys_mergeable()) I can send a patch to drop __BIOVEC_PHYS_MERGEABLE. Regards,
diff --git a/drivers/xen/biomerge.c b/drivers/xen/biomerge.c index 0edb91c..20387c2 100644 --- a/drivers/xen/biomerge.c +++ b/drivers/xen/biomerge.c @@ -9,6 +9,9 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1, unsigned long mfn1 = pfn_to_mfn(page_to_pfn(vec1->bv_page)); unsigned long mfn2 = pfn_to_mfn(page_to_pfn(vec2->bv_page)); + /* TODO: Implement it correctly */ + return 0; + return __BIOVEC_PHYS_MERGEABLE(vec1, vec2) && ((mfn1 == mfn2) || ((mfn1+1) == mfn2)); }
When Linux is using 64K page granularity, every page will be slipt in multiple non-contiguous 4K MFN. I'm not sure how to handle efficiently the check to know whether we can merge 2 biovec with a such case. So for now, always says that biovec are not mergeable. Signed-off-by: Julien Grall <julien.grall@citrix.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: David Vrabel <david.vrabel@citrix.com> --- drivers/xen/biomerge.c | 3 +++ 1 file changed, 3 insertions(+)