| Message ID | 20200129101643.1394-3-pdurrant@amazon.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | purge free_shared_domheap_page() | expand |
On 29.01.2020 11:16, Paul Durrant wrote: > Currently the function will pointlessly acquire and release the global > 'heap_lock' in this case. > > NOTE: No caller yet calls domain_adjust_tot_pages() with a zero 'pages' > argument, but a subsequent patch will make this possible. With this memory_exchange(), as previously indicated, now needlessly prevents the call when !dec_count. I do think, as said there, that together with the addition here then redundant checks in callers should be dropped (and as it looks the named one is the only one). Jan
> -----Original Message----- > From: Jan Beulich <jbeulich@suse.com> > Sent: 29 January 2020 11:13 > To: Durrant, Paul <pdurrant@amazon.co.uk> > Cc: xen-devel@lists.xenproject.org; Andrew Cooper > <andrew.cooper3@citrix.com>; George Dunlap <George.Dunlap@eu.citrix.com>; > Ian Jackson <ian.jackson@eu.citrix.com>; Julien Grall <julien@xen.org>; > Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; Stefano Stabellini > <sstabellini@kernel.org>; Wei Liu <wl@xen.org> > Subject: Re: [PATCH v5 2/4] mm: modify domain_adjust_tot_pages() to better > handle a zero adjustment > > On 29.01.2020 11:16, Paul Durrant wrote: > > Currently the function will pointlessly acquire and release the global > > 'heap_lock' in this case. > > > > NOTE: No caller yet calls domain_adjust_tot_pages() with a zero 'pages' > > argument, but a subsequent patch will make this possible. > > With this memory_exchange(), as previously indicated, now needlessly > prevents the call when !dec_count. I do think, as said there, that > together with the addition here then redundant checks in callers > should be dropped (and as it looks the named one is the only one). > Ok, yes I missed that. Paul > Jan
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c index 919a270587..135e15bae0 100644 --- a/xen/common/page_alloc.c +++ b/xen/common/page_alloc.c @@ -460,6 +460,9 @@ unsigned long domain_adjust_tot_pages(struct domain *d, long pages) { long dom_before, dom_after, dom_claimed, sys_before, sys_after; + if ( !pages ) + goto out; + ASSERT(spin_is_locked(&d->page_alloc_lock)); d->tot_pages += pages;
Currently the function will pointlessly acquire and release the global 'heap_lock' in this case. NOTE: No caller yet calls domain_adjust_tot_pages() with a zero 'pages' argument, but a subsequent patch will make this possible. Signed-off-by: Paul Durrant <pdurrant@amazon.com> --- Cc: Andrew Cooper <andrew.cooper3@citrix.com> Cc: George Dunlap <George.Dunlap@eu.citrix.com> Cc: Ian Jackson <ian.jackson@eu.citrix.com> Cc: Jan Beulich <jbeulich@suse.com> Cc: Julien Grall <julien@xen.org> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Stefano Stabellini <sstabellini@kernel.org> Cc: Wei Liu <wl@xen.org> v5: - Split out from the subsequent 'make MEMF_no_refcount pages safe to assign' patch as requested by Jan --- xen/common/page_alloc.c | 3 +++ 1 file changed, 3 insertions(+)