| Message ID | 20220913093256.22880-3-jgross@suse.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | xen/gnttab: reduce size of struct active_grant_entry | expand |
On 15.09.22 13:50, Jan Beulich wrote: > On 13.09.2022 11:32, Juergen Gross wrote: >> The size of struct active_grant_entry for 64-bit builds is 40 or 48 >> bytes today (with or without NDEBUG). >> >> It can easily be reduced by 8 bytes by replacing the trans_domain >> pointer with the domid of the related domain. trans_domain is only ever >> used for transitive grants, which doesn't have any known users. >> >> This reduction will result in less memory usage and (for production >> builds) in faster code, as indexing into the active_grant_entry array >> will be much easier with an entry having a power-of-2 size. >> >> The performance loss when using transitive grants shouldn't really >> matter, given the probability that those aren't in use at all. >> >> Signed-off-by: Juergen Gross <jgross@suse.com> >> --- >> V2: >> - rename trans_domid to src_domid (Jan Beulich) >> --- >> xen/common/grant_table.c | 13 +++++++------ >> 1 file changed, 7 insertions(+), 6 deletions(-) >> >> diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c >> index fba329dcc2..59342df3b7 100644 >> --- a/xen/common/grant_table.c >> +++ b/xen/common/grant_table.c >> @@ -381,13 +381,13 @@ struct active_grant_entry { >> }) >> >> domid_t domid; /* Domain being granted access. */ >> + domid_t src_domid; /* Domain granting access. */ > > I'm afraid I still view the comment as ambiguous, for there being two > domains involved in granting access for transitive grants. Preferably > with e.g "Original" added (which of course could be done by the > committer, provided this isn't lost by the time 4.18 opens), > Reviewed-by: Jan Beulich <jbeulich@suse.com> Thanks. I'll just send an updated V3 (probably tomorrow). Juergen
diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c index fba329dcc2..59342df3b7 100644 --- a/xen/common/grant_table.c +++ b/xen/common/grant_table.c @@ -381,13 +381,13 @@ struct active_grant_entry { }) domid_t domid; /* Domain being granted access. */ + domid_t src_domid; /* Domain granting access. */ unsigned int start:15; /* For sub-page grants, the start offset in the page. */ bool is_sub_page:1; /* True if this is a sub-page grant. */ unsigned int length:16; /* For sub-page grants, the length of the grant. */ grant_ref_t trans_gref; - struct domain *trans_domain; mfn_t mfn; /* Machine frame being granted. */ #ifndef NDEBUG gfn_t gfn; /* Guest's idea of the frame being granted. */ @@ -1095,7 +1095,7 @@ map_grant_ref( act->start = 0; act->length = PAGE_SIZE; act->is_sub_page = false; - act->trans_domain = rd; + act->src_domid = rd->domain_id; act->trans_gref = ref; } } @@ -2494,7 +2494,8 @@ release_grant_for_copy( else { status = &status_entry(rgt, gref); - td = act->trans_domain; + td = (act->src_domid == rd->domain_id) + ? rd : knownalive_domain_from_domid(act->src_domid); trans_gref = act->trans_gref; } @@ -2657,7 +2658,7 @@ acquire_grant_for_copy( !mfn_eq(act->mfn, grant_mfn) || act->start != trans_page_off || act->length != trans_length || - act->trans_domain != td || + act->src_domid != td->domain_id || act->trans_gref != trans_gref || !act->is_sub_page)) ) { @@ -2676,7 +2677,7 @@ acquire_grant_for_copy( act->domid = ldom; act->start = trans_page_off; act->length = trans_length; - act->trans_domain = td; + act->src_domid = td->domain_id; act->trans_gref = trans_gref; act->mfn = grant_mfn; act_set_gfn(act, INVALID_GFN); @@ -2738,7 +2739,7 @@ acquire_grant_for_copy( act->is_sub_page = is_sub_page; act->start = trans_page_off; act->length = trans_length; - act->trans_domain = td; + act->src_domid = td->domain_id; act->trans_gref = trans_gref; act->mfn = grant_mfn; }
The size of struct active_grant_entry for 64-bit builds is 40 or 48 bytes today (with or without NDEBUG). It can easily be reduced by 8 bytes by replacing the trans_domain pointer with the domid of the related domain. trans_domain is only ever used for transitive grants, which doesn't have any known users. This reduction will result in less memory usage and (for production builds) in faster code, as indexing into the active_grant_entry array will be much easier with an entry having a power-of-2 size. The performance loss when using transitive grants shouldn't really matter, given the probability that those aren't in use at all. Signed-off-by: Juergen Gross <jgross@suse.com> --- V2: - rename trans_domid to src_domid (Jan Beulich) --- xen/common/grant_table.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)