Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [RFC] [PATCH 0/5] Dynamically allocated pageflags. | Date | Tue, 24 Jul 2007 11:47:05 +0200 |
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On Tuesday, 24 July 2007 00:27, Nigel Cunningham wrote: > 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.
Well, that's what I'm really interested in.
> Do you see advantages to snapshot.c that I might have missed?
Not at the moment, but I need to have a closer look.
Greetings, Rafael
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