| Message ID | 20180530061212.84915-1-gthelen@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, May 29, 2018 at 11:12 PM Greg Thelen <gthelen@google.com> wrote: > > Use smaller scan_control fields for order, priority, and reclaim_idx. > Convert fields from int => s8. All easily fit within a byte: > * allocation order range: 0..MAX_ORDER(64?) > * priority range: 0..12(DEF_PRIORITY) > * reclaim_idx range: 0..6(__MAX_NR_ZONES) > > Since commit 6538b8ea886e ("x86_64: expand kernel stack to 16K") x86_64 > stack overflows are not an issue. But it's inefficient to use ints. > > Use s8 (signed byte) rather than u8 to allow for loops like: > do { > ... > } while (--sc.priority >= 0); > > Add BUILD_BUG_ON to verify that s8 is capable of storing max values. > > This reduces sizeof(struct scan_control): > * 96 => 80 bytes (x86_64) > * 68 => 56 bytes (i386) > > scan_control structure field order is changed to utilize padding. > After this patch there is 1 bit of scan_control padding. > > Signed-off-by: Greg Thelen <gthelen@google.com> > Suggested-by: Matthew Wilcox <willy@infradead.org> Is there any interest in this? Less stack usage could mean less dcache and dtlb pressure. But I understand if the complexity is distasteful. > --- > mm/vmscan.c | 32 ++++++++++++++++++++------------ > 1 file changed, 20 insertions(+), 12 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 9b697323a88c..42731faea306 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -65,12 +65,6 @@ struct scan_control { > /* How many pages shrink_list() should reclaim */ > unsigned long nr_to_reclaim; > > - /* This context's GFP mask */ > - gfp_t gfp_mask; > - > - /* Allocation order */ > - int order; > - > /* > * Nodemask of nodes allowed by the caller. If NULL, all nodes > * are scanned. > @@ -83,12 +77,6 @@ struct scan_control { > */ > struct mem_cgroup *target_mem_cgroup; > > - /* Scan (total_size >> priority) pages at once */ > - int priority; > - > - /* The highest zone to isolate pages for reclaim from */ > - enum zone_type reclaim_idx; > - > /* Writepage batching in laptop mode; RECLAIM_WRITE */ > unsigned int may_writepage:1; > > @@ -111,6 +99,18 @@ struct scan_control { > /* One of the zones is ready for compaction */ > unsigned int compaction_ready:1; > > + /* Allocation order */ > + s8 order; > + > + /* Scan (total_size >> priority) pages at once */ > + s8 priority; > + > + /* The highest zone to isolate pages for reclaim from */ > + s8 reclaim_idx; > + > + /* This context's GFP mask */ > + gfp_t gfp_mask; > + > /* Incremented by the number of inactive pages that were scanned */ > unsigned long nr_scanned; > > @@ -3047,6 +3047,14 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order, > .may_swap = 1, > }; > > + /* > + * scan_control uses s8 fields for order, priority, and reclaim_idx. > + * Confirm they are large enough for max values. > + */ > + BUILD_BUG_ON(MAX_ORDER > S8_MAX); > + BUILD_BUG_ON(DEF_PRIORITY > S8_MAX); > + BUILD_BUG_ON(MAX_NR_ZONES > S8_MAX); > + > /* > * Do not enter reclaim if fatal signal was delivered while throttled. > * 1 is returned so that the page allocator does not OOM kill at this > -- > 2.17.0.921.gf22659ad46-goog >
diff --git a/mm/vmscan.c b/mm/vmscan.c index 9b697323a88c..42731faea306 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -65,12 +65,6 @@ struct scan_control { /* How many pages shrink_list() should reclaim */ unsigned long nr_to_reclaim; - /* This context's GFP mask */ - gfp_t gfp_mask; - - /* Allocation order */ - int order; - /* * Nodemask of nodes allowed by the caller. If NULL, all nodes * are scanned. @@ -83,12 +77,6 @@ struct scan_control { */ struct mem_cgroup *target_mem_cgroup; - /* Scan (total_size >> priority) pages at once */ - int priority; - - /* The highest zone to isolate pages for reclaim from */ - enum zone_type reclaim_idx; - /* Writepage batching in laptop mode; RECLAIM_WRITE */ unsigned int may_writepage:1; @@ -111,6 +99,18 @@ struct scan_control { /* One of the zones is ready for compaction */ unsigned int compaction_ready:1; + /* Allocation order */ + s8 order; + + /* Scan (total_size >> priority) pages at once */ + s8 priority; + + /* The highest zone to isolate pages for reclaim from */ + s8 reclaim_idx; + + /* This context's GFP mask */ + gfp_t gfp_mask; + /* Incremented by the number of inactive pages that were scanned */ unsigned long nr_scanned; @@ -3047,6 +3047,14 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order, .may_swap = 1, }; + /* + * scan_control uses s8 fields for order, priority, and reclaim_idx. + * Confirm they are large enough for max values. + */ + BUILD_BUG_ON(MAX_ORDER > S8_MAX); + BUILD_BUG_ON(DEF_PRIORITY > S8_MAX); + BUILD_BUG_ON(MAX_NR_ZONES > S8_MAX); + /* * Do not enter reclaim if fatal signal was delivered while throttled. * 1 is returned so that the page allocator does not OOM kill at this
Use smaller scan_control fields for order, priority, and reclaim_idx. Convert fields from int => s8. All easily fit within a byte: * allocation order range: 0..MAX_ORDER(64?) * priority range: 0..12(DEF_PRIORITY) * reclaim_idx range: 0..6(__MAX_NR_ZONES) Since commit 6538b8ea886e ("x86_64: expand kernel stack to 16K") x86_64 stack overflows are not an issue. But it's inefficient to use ints. Use s8 (signed byte) rather than u8 to allow for loops like: do { ... } while (--sc.priority >= 0); Add BUILD_BUG_ON to verify that s8 is capable of storing max values. This reduces sizeof(struct scan_control): * 96 => 80 bytes (x86_64) * 68 => 56 bytes (i386) scan_control structure field order is changed to utilize padding. After this patch there is 1 bit of scan_control padding. Signed-off-by: Greg Thelen <gthelen@google.com> Suggested-by: Matthew Wilcox <willy@infradead.org> --- mm/vmscan.c | 32 ++++++++++++++++++++------------ 1 file changed, 20 insertions(+), 12 deletions(-)