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SubjectRe: [RFC 7/8] Enhance ramfs to support higher order pages
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On (19/04/07 09:35), Christoph Lameter didst pronounce:
> Variable Order Page Cache: Add support to ramfs
>
> 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.
>
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
>
> ---
> fs/ramfs/file-mmu.c | 11 +++++++++++
> fs/ramfs/inode.c | 15 ++++++++++++---
> include/linux/ramfs.h | 1 +
> 3 files changed, 24 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 2007-04-18 21:46:38.000000000 -0700
> +++ linux-2.6.21-rc7/fs/ramfs/file-mmu.c 2007-04-18 22:02:03.000000000 -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 2007-04-18 21:46:38.000000000 -0700
> +++ linux-2.6.21-rc7/fs/ramfs/inode.c 2007-04-18 22:02:03.000000000 -0700
> @@ -61,6 +61,7 @@ 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;
> + inode->i_mapping->order = 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 +69,10 @@ 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 (inode->i_mapping->order)
> + inode->i_fop = &ramfs_file_higher_order_operations;
> + else
> + inode->i_fop = &ramfs_file_operations;

So the difference here appears to be that specifying an order means you
can't mmap(). right?

That's fair enough for the moment but relaxing would make ramfs
potentially usable as a replacement for hugetlbfs so there would be just
one ram-based filesystem instead of two.

> break;
> case S_IFDIR:
> inode->i_op = &ramfs_dir_inode_operations;
> @@ -164,10 +168,15 @@ 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);
>

Not the nicest option there but no harm for the moment.

> 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 2007-04-18 21:46:38.000000000 -0700
> +++ linux-2.6.21-rc7/include/linux/ramfs.h 2007-04-18 22:02:03.000000000 -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);
>

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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