The simplest file system to use is ramfs. Add a mount parameter that specifies the page order of the pages that ramfs should use. If the order is greater than zero then disable mmap functionality. This could be removed if the VM would be changes to support faulting higher order pages but for now we are content with buffered I/O on higher order pages. Note that ramfs does not use the lower layers (buffer I/O etc) so its the safest to use right now. If you apply this patch and then you can f.e. try this: mount -tramfs -o10 none /media Mounts a ramfs filesystem with order 10 pages (4 MB) cp linux-2.6.21-rc7.tar.gz /media Populate the ramfs. Note that we allocate 14 pages of 4M each instead of 13508.. umount /media Gets rid of the large pages again Signed-off-by: Christoph Lameter --- fs/ramfs/file-mmu.c | 11 +++++++++++ fs/ramfs/inode.c | 16 +++++++++++++--- include/linux/ramfs.h | 1 + 3 files changed, 25 insertions(+), 3 deletions(-) Index: linux-2.6.21-rc7/fs/ramfs/file-mmu.c =================================================================== --- linux-2.6.21-rc7.orig/fs/ramfs/file-mmu.c 2007-04-23 22:26:18.000000000 -0700 +++ linux-2.6.21-rc7/fs/ramfs/file-mmu.c 2007-04-23 22:27:51.000000000 -0700 @@ -45,6 +45,17 @@ const struct file_operations ramfs_file_ .llseek = generic_file_llseek, }; +/* Higher order mappings do not support mmmap */ +const struct file_operations ramfs_file_higher_order_operations = { + .read = do_sync_read, + .aio_read = generic_file_aio_read, + .write = do_sync_write, + .aio_write = generic_file_aio_write, + .fsync = simple_sync_file, + .sendfile = generic_file_sendfile, + .llseek = generic_file_llseek, +}; + const struct inode_operations ramfs_file_inode_operations = { .getattr = simple_getattr, }; Index: linux-2.6.21-rc7/fs/ramfs/inode.c =================================================================== --- linux-2.6.21-rc7.orig/fs/ramfs/inode.c 2007-04-23 22:26:18.000000000 -0700 +++ linux-2.6.21-rc7/fs/ramfs/inode.c 2007-04-23 22:33:23.000000000 -0700 @@ -61,6 +61,8 @@ struct inode *ramfs_get_inode(struct sup inode->i_blocks = 0; inode->i_mapping->a_ops = &ramfs_aops; inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info; + set_mapping_order(inode->i_mapping, + sb->s_blocksize_bits - PAGE_CACHE_SHIFT); inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; switch (mode & S_IFMT) { default: @@ -68,7 +70,10 @@ struct inode *ramfs_get_inode(struct sup break; case S_IFREG: inode->i_op = &ramfs_file_inode_operations; - inode->i_fop = &ramfs_file_operations; + if (mapping_order(inode->i_mapping)) + inode->i_fop = &ramfs_file_higher_order_operations; + else + inode->i_fop = &ramfs_file_operations; break; case S_IFDIR: inode->i_op = &ramfs_dir_inode_operations; @@ -164,10 +169,15 @@ static int ramfs_fill_super(struct super { struct inode * inode; struct dentry * root; + int order = 0; + char *options = data; + + if (options && *options) + order = simple_strtoul(options, NULL, 10); sb->s_maxbytes = MAX_LFS_FILESIZE; - sb->s_blocksize = PAGE_CACHE_SIZE; - sb->s_blocksize_bits = PAGE_CACHE_SHIFT; + sb->s_blocksize = PAGE_CACHE_SIZE << order; + sb->s_blocksize_bits = order + PAGE_CACHE_SHIFT; sb->s_magic = RAMFS_MAGIC; sb->s_op = &ramfs_ops; sb->s_time_gran = 1; Index: linux-2.6.21-rc7/include/linux/ramfs.h =================================================================== --- linux-2.6.21-rc7.orig/include/linux/ramfs.h 2007-04-23 22:26:18.000000000 -0700 +++ linux-2.6.21-rc7/include/linux/ramfs.h 2007-04-23 22:27:51.000000000 -0700 @@ -16,6 +16,7 @@ extern int ramfs_nommu_mmap(struct file #endif extern const struct file_operations ramfs_file_operations; +extern const struct file_operations ramfs_file_higher_order_operations; extern struct vm_operations_struct generic_file_vm_ops; extern int __init init_rootfs(void); -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/