On 06/22/2010 04:48 AM, Dan Magenheimer wrote: > [PATCH V3 0/8] Cleancache: overview > <snip> > > Documentation/ABI/testing/sysfs-kernel-mm-cleancache | 11 + > Documentation/vm/cleancache.txt | 194 +++++++++++++++++++ > fs/btrfs/extent_io.c | 9 > fs/btrfs/super.c | 2 > fs/buffer.c | 5 > fs/ext3/super.c | 2 > fs/ext4/super.c | 2 > fs/mpage.c | 7 > fs/ocfs2/super.c | 3 > fs/super.c | 7 > include/linux/cleancache.h | 88 ++++++++ > include/linux/fs.h | 5 > mm/Kconfig | 22 ++ > mm/Makefile | 1 > mm/cleancache.c | 169 ++++++++++++++++ > mm/filemap.c | 11 + > mm/truncate.c | 10 > 17 files changed, 548 insertions(+) > > (following is a copy of Documentation/vm/cleancache.txt) > > MOTIVATION > > Cleancache can be thought of as a page-granularity victim cache for clean > pages that the kernel's pageframe replacement algorithm (PFRA) would like > to keep around, but can't since there isn't enough memory. So when the > PFRA "evicts" a page, it first attempts to put it into a synchronous > concurrency-safe page-oriented "pseudo-RAM" device (such as Xen's Transcendent > Memory, aka "tmem", or in-kernel compressed memory, aka "zmem", or other > RAM-like devices) which is not directly accessible or addressable by the > kernel and is of unknown and possibly time-varying size. And when a > cleancache-enabled filesystem wishes to access a page in a file on disk, > it first checks cleancache to see if it already contains it; if it does, > the page is copied into the kernel and a disk access is avoided. > Since zcache is now one of its use cases, I think the major objection that remains against cleancache is its intrusiveness -- in particular, need to change individual filesystems (even though one liners). Changes below should help avoid these per-fs changes and make it more self contained. I haven't tested these changes myself, so there might be missed cases or other mysterious problems: 1. Cleancache requires filesystem specific changes primarily to make a call to cleancache init and store (per-fs instance) pool_id. I think we can get rid of these by directly passing 'struct super_block' pointer which is also sufficient to identify FS instance a page belongs to. This should then be used as a 'handle' by cleancache_ops provider to find corresponding memory pool or create a new pool when a new handle is encountered. This leaves out case of ocfs2 for which cleancache needs 'uuid' to decide if a shared pool should be created. IMHO, this case (and cleancache.init_shared_fs) should be removed from cleancache_ops since it is applicable only for Xen's cleancache_ops provider. 2. I think change in btrfs can be avoided by moving cleancache_get_page() from do_mpage_reapage() to filemap_fault() and this should work for all filesystems. See: handle_pte_fault() -> do_(non)linear_fault() -> __do_fault() -> vma->vm_ops->fault() which is defined as filemap_fault() for all filesystems. If some future filesystem uses its own custom function (why?) then it will have to arrange for call to cleancache_get_page(), if it wants this feature. With above changes, cleancache will be fairly self-contained: - cleancache_put_page() when page is removed from page-cache - cleacacache_get_page() when PF occurs (and after page-cache is searched) - cleancache_flush_*() on truncate_*() Thanks, Nitin -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
