On 10/4/2012 2:23 PM, David Miller wrote: > From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > Date: Thu, 04 Oct 2012 22:00:48 +0530 > >> David Miller <davem@xxxxxxxxxxxxx> writes: >> >>> We've split up the PTE tables so that they take up half a page instead >>> of a full page. This is in order to facilitate transparent huge page >>> support, which works much better if our PMDs cover 4MB instead of 8MB. >>> >>> What we do is have a one-behind cache for PTE table allocations in the >>> mm struct. >>> >>> This logic triggers only on allocations. For example, we don't try to >>> keep track of free'd up page table blocks in the style that the s390 >>> port does. >> >> I am also implementing a similar change for powerpc. We have a 64K page >> size, and want to make sure PMD cover 16MB, which is the huge page size >> supported by the hardware. I was looking at using the s390 logic, >> considering we have 16 PMDs mapping to same PTE page. Should we look at >> generalizing the case so that other architectures can start using the >> same code ? > > I think until we have multiple cases we won't know what's common or not. > > Each arch has different need. I need to split the page into two pieces > so my code is simpler, and juse uses page counting to manage alloc/free. > > Whereas s390 uses an bitmask to manage page state, and also reclaims > pgtable pages into a per-mm list on free. I decided not to do that > and to just let the page allocator do the work. > > So I don't think it's appropriate to think about commonization at this > time, as even the only two cases existing are very non-common :-) I'll add arch/tile to the list of architectures that would benefit. We currently allocate PTEs using the page allocator, but by default we use 64K pages and 16M huge pages, so with 8-byte PTEs that's just 2K for the page table, so we could fit 32 of them on a page if we wished. Instead, for the time being, we just waste the space. -- Chris Metcalf, Tilera Corp. http://www.tilera.com -- 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>