On Wed, May 29, 2013 at 04:53:12PM +0200, Andres Freund wrote: > On 2013-02-16 14:53:43 +1030, Rusty Russell wrote: > > Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: > > > On Fri, 15 Feb 2013 18:13:04 -0500 > > > Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > >> I dunno. The byte vector might not be optimal but its worst cases > > >> seem more attractive, is just as extensible, and dead simple to use. > > > > > > But I think "which pages from this 4TB file are in core" will not be an > > > uncommon usage, and writing a gig of memory to find three pages is just > > > awful. > > > > Actually, I don't know of any usage for this call. > > [months later, catching up] > > I do. Postgres' could really use something like that for making saner > assumptions about the cost of doing an index/heap scan. postgres doesn't > use mmap() and mmaping larger files into memory isn't all that cheap > (32bit...) so having fincore would be nice. How much of the areas you want to use it against is usually cached? I.e. are those 4TB files with 3 cached pages? I do wonder if we should just have two separate interfaces. Ugly, but I don't really see how the two requirements (dense but many holes vs. huge sparse areas) could be acceptably met with one interface. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>