Messages in this thread | | | Date | Wed, 20 Sep 2017 19:37:12 -0600 | From | Tycho Andersen <> | Subject | Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) |
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On Wed, Sep 20, 2017 at 05:27:02PM -0700, Dave Hansen wrote: > On 09/20/2017 05:09 PM, Tycho Andersen wrote: > >> I think the only thing that will really help here is if you batch the > >> allocations. For instance, you could make sure that the per-cpu-pageset > >> lists always contain either all kernel or all user data. Then remap the > >> entire list at once and do a single flush after the entire list is consumed. > > Just so I understand, the idea would be that we only flush when the > > type of allocation alternates, so: > > > > kmalloc(..., GFP_KERNEL); > > kmalloc(..., GFP_KERNEL); > > /* remap+flush here */ > > kmalloc(..., GFP_HIGHUSER); > > /* remap+flush here */ > > kmalloc(..., GFP_KERNEL); > > Not really. We keep a free list per migrate type, and a per_cpu_pages > (pcp) list per migratetype: > > > struct per_cpu_pages { > > int count; /* number of pages in the list */ > > int high; /* high watermark, emptying needed */ > > int batch; /* chunk size for buddy add/remove */ > > > > /* Lists of pages, one per migrate type stored on the pcp-lists */ > > struct list_head lists[MIGRATE_PCPTYPES]; > > }; > > The migratetype is derived from the GFP flags in > gfpflags_to_migratetype(). In general, GFP_HIGHUSER and GFP_KERNEL come > from different migratetypes, so they come from different free lists. > > In your case above, the GFP_HIGHUSER allocation come through the > MIGRATE_MOVABLE pcp list while the GFP_KERNEL ones come from the > MIGRATE_UNMOVABLE one. Since we add a bunch of pages to those lists at > once, you could do all the mapping/unmapping/flushing on a bunch of > pages at once > > Or, you could hook your code into the places where the migratetype of > memory is changed (set_pageblock_migratetype(), plus where we fall > back). Those changes are much more rare than page allocation.
I see, thanks for all this discussion. It has been very helpful!
Tycho
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