On 03/20/2018 03:11 PM, Aaron Lu wrote: > On Tue, Mar 20, 2018 at 12:45:50PM +0100, Vlastimil Babka wrote: >> But why, with all the prefetching in place? > > The prefetch is just for its order 0 buddy, if merge happens, then its > order 1 buddy will also be checked and on and on, so the cache misses > are much more in merge mode. I see. >> Not thrilled about such disruptive change in the name of a >> microbenchmark :/ Shouldn't normally the pcplists hide the overhead? > > Sadly, with the default pcp count, it didn't avoid the lock contention. > We can of course increase pcp->count to a large enough value to avoid > entering buddy and thus avoid zone->lock contention, but that would > require admin to manually change the value on a per-machine per-workload > basis I believe. Well, anyone who really cares about performance has to invest some time to tuning anyway, I believe? >> If not, wouldn't it make more sense to turn zone->lock into a range lock? > > Not familiar with range lock, will need to take a look at it, thanks for > the pointer. The suggestion was rather quick and not well thought-out. Range lock itself is insufficient - for merging/splitting buddies it's ok for working with struct pages because the candidate buddies are within a MAX_ORDER range. But the freelists contain pages from the whole zone. >> >>> A new document file called "struct_page_filed" is added to explain >>> the newly reused field in "struct page". >> >> Sounds rather ad-hoc for a single field, I'd rather document it via >> comments. > > Dave would like to have a document to explain all those "struct page" > fields that are repurposed under different scenarios and this is the > very start of the document :-) Oh, I see. > I probably should have explained the intent of the document more. > > Thanks for taking a look at this. > >>> Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx> >>> Signed-off-by: Aaron Lu <aaron.lu@xxxxxxxxx> >>> --- >>> Documentation/vm/struct_page_field | 5 +++ >>> include/linux/mm_types.h | 1 + >>> mm/compaction.c | 13 +++++- >>> mm/internal.h | 27 ++++++++++++ >>> mm/page_alloc.c | 89 +++++++++++++++++++++++++++++++++----- >>> 5 files changed, 122 insertions(+), 13 deletions(-) >>> create mode 100644 Documentation/vm/struct_page_field >>>
