On Mon 05-08-13 12:43:58, Andy Lutomirski wrote: > My application fallocates and mmaps (shared, writable) a lot (several > GB) of data at startup. Those mappings are mlocked, and they live on > ext4. The first write to any given page is slow because > ext4_da_get_block_prep can block. This means that, to get decent > performance, I need to write something to all of these pages at > startup. This, in turn, causes a giant IO storm as several GB of > zeros get pointlessly written to disk. > > This series is an attempt to add madvise(..., MADV_WILLWRITE) to > signal to the kernel that I will eventually write to the referenced > pages. It should cause any expensive operations that happen on the > first write to happen immediately, but it should not result in > dirtying the pages. > > madvice(addr, len, MADV_WILLWRITE) returns the number of bytes that > the operation succeeded on or a negative error code if there was an > actual failure. A return value of zero signifies that the kernel > doesn't know how to "willwrite" the range and that userspace should > implement a fallback. > > For now, it only works on shared writable ext4 mappings. Eventually > it should support other filesystems as well as private pages (it > should COW the pages but not cause swap IO) and anonymous pages (it > should COW the zero page if applicable). > > The implementation leaves much to be desired. In particular, it > generates dirty buffer heads on a clean page, and this scares me. > > Thoughts? One question before I look at the patches: Why don't you use fallocate() in your application? The functionality you require seems to be pretty similar to it - writing to an already allocated block is usually quick. Honza > Andy Lutomirski (3): > mm: Add MADV_WILLWRITE to indicate that a range will be written to > fs: Add block_willwrite > ext4: Implement willwrite for the delalloc case > > fs/buffer.c | 57 ++++++++++++++++++++++++++++++++++ > fs/ext4/ext4.h | 2 ++ > fs/ext4/file.c | 1 + > fs/ext4/inode.c | 22 +++++++++++++ > include/linux/buffer_head.h | 3 ++ > include/linux/mm.h | 12 +++++++ > include/uapi/asm-generic/mman-common.h | 3 ++ > mm/madvise.c | 28 +++++++++++++++-- > 8 files changed, 126 insertions(+), 2 deletions(-) > > -- > 1.8.3.1 > > -- > 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 -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
