Messages in this thread |  | | Subject | Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) | From | Dave Hansen <> | Date | Wed, 20 Sep 2017 17:27:02 -0700 |
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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.
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