Hi. On Tuesday 24 July 2007 08:05:21 Rafael J. Wysocki wrote: > Hi, > > On Monday, 23 July 2007 15:05, Nigel Cunningham wrote: > > Hi all. > > > > As we all know, pageflags have been a scarce resource for a while now. These > > patches seek to help address that issue by adding support for a new type > > of 'dynamically allocated' pageflag. > > > > The basic idea is that we use per node & zone bitmaps built out of order zero > > allocations, to replace bits in page->flags. Bitmaps can be sparse, being > > populated when a bit on the page is set, and returning zero for all bits in > > sparse pages. Untested hotplug support is included. > > > > This method of storing the data does of course come with a performance hit. > > I've included some simple timing loops in #ifdef'd code that help quantify > > that. > > > > Interestingly, the new implementation is actually quicker under some > > circumstances. In cases where the usage pattern involves operating on the > > flags for a number of pages in succession, the hit involved in getting the > > struct pages from main memory appears to be greater than that involved in > > calculating which unsigned long and bit to test. > > > > Tested only on UP (x86_64) so far. > > How does it compare to the memory bitmaps used by swsusp, defined in > kernel/power/snapshot.c? Looking through kernel/power/snapshot.c, I'd say this implementation has advantages in having support for memory hotplugging, sparseness and random access to the flags in the bitmap. Like the snapshot.c implementation, it uses per-zone bitmaps and has a method that can be used to iterate over the contents of a bitmap. Having per-node support might also be useful. I haven't looked at the speed of the snapshot.c implementation. Do you see advantages to snapshot.c that I might have missed? Regards, Nigel -- See http://www.tuxonice.net for Howtos, FAQs, mailing lists, wiki and bugzilla info.
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