On Sat, Mar 15, 2014 at 10:46:13PM -0400, Matthew Wilcox wrote: > On Sat, Mar 15, 2014 at 01:32:33AM +0200, Kirill A. Shutemov wrote: > > Side note: I'm sceptical about whole idea to use i_mmap_mutux to protect > > against truncate. It will not scale good enough comparing lock_page() > > with its granularity. > > I'm actually working on this now. The basic idea is to put an entry in > the radix tree for each page. For zero pages, that's a pagecache page. > For pages that map to the media, it's an exceptional entry. Radix tree > exceptional entries take two bits, leaving us with 30 or 62 bits depending > on sizeof(void *). We can then take two more bits for Dirty and Lock, > leaving 28 or 60 bits that we can use to cache the PFN on the page, > meaning that we won't have to call the filesystem's get_block as often. Sound reasonable to me. Implementation of ->map_pages should be trivial with this. Few questions: - why would you need Dirty for DAX? - are you sure that 28 bits is enough for PFN everywhere? ARM with LPAE can have up to 40 physical address lines. Is there any 32-bit machine with more address lines? -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
