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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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