--- /dev/null
+
+From: David Howells <dhowells@redhat.com>
+
+The attached patch replaces backing_dev_info::memory_backed with capabilitied
+bitmap. The capabilities available include:
+
+ (*) BDI_CAP_NO_ACCT_DIRTY
+
+ Set if the pages associated with this backing device should not be
+ tracked by the dirty page accounting.
+
+ (*) BDI_CAP_NO_WRITEBACK
+
+ Set if dirty pages associated with this backing device should not have
+ writepage() or writepages() invoked upon them to clean them.
+
+ (*) Capability markers that indicate what a backing device is capable of
+ with regard to memory mapping facilities. These flags indicate whether a
+ device can be mapped directly, whether it can be copied for a mapping,
+ and whether direct mappings can be read, written and/or executed. This
+ information is primarily aimed at improving no-MMU private mapping
+ support.
+
+The patch also provides convenience functions for determining the dirty-page
+capabilities available on backing devices directly or on the backing devices
+associated with a mapping. These are provided to keep line length down when
+checking for the capabilities.
+
+Signed-Off-By: David Howells <dhowells@redhat.com>
+Signed-off-by: Andrew Morton <akpm@osdl.org>
+---
+
+ 25-akpm/drivers/block/ll_rw_blk.c | 2 -
+ 25-akpm/drivers/block/rd.c | 4 +--
+ 25-akpm/drivers/char/mem.c | 6 +++++
+ 25-akpm/fs/buffer.c | 2 -
+ 25-akpm/fs/fs-writeback.c | 4 +--
+ 25-akpm/fs/hugetlbfs/inode.c | 2 -
+ 25-akpm/fs/ramfs/inode.c | 4 ++-
+ 25-akpm/fs/sysfs/inode.c | 2 -
+ 25-akpm/include/linux/backing-dev.h | 41 +++++++++++++++++++++++++++++++++++-
+ 25-akpm/mm/filemap.c | 6 ++---
+ 25-akpm/mm/page-writeback.c | 6 ++---
+ 25-akpm/mm/readahead.c | 1
+ 25-akpm/mm/shmem.c | 4 +--
+ 25-akpm/mm/swap_state.c | 2 -
+ 14 files changed, 67 insertions(+), 19 deletions(-)
+
+diff -puN drivers/block/ll_rw_blk.c~bdi-provide-backing-device-capability-information drivers/block/ll_rw_blk.c
+--- 25/drivers/block/ll_rw_blk.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/drivers/block/ll_rw_blk.c Tue Mar 8 16:33:20 2005
+@@ -238,7 +238,7 @@ void blk_queue_make_request(request_queu
+ q->make_request_fn = mfn;
+ q->backing_dev_info.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+ q->backing_dev_info.state = 0;
+- q->backing_dev_info.memory_backed = 0;
++ q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
+ blk_queue_max_sectors(q, MAX_SECTORS);
+ blk_queue_hardsect_size(q, 512);
+ blk_queue_dma_alignment(q, 511);
+diff -puN drivers/block/rd.c~bdi-provide-backing-device-capability-information drivers/block/rd.c
+--- 25/drivers/block/rd.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/drivers/block/rd.c Tue Mar 8 16:33:20 2005
+@@ -325,7 +325,7 @@ static int rd_ioctl(struct inode *inode,
+ */
+ static struct backing_dev_info rd_backing_dev_info = {
+ .ra_pages = 0, /* No readahead */
+- .memory_backed = 1, /* Does not contribute to dirty memory */
++ .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK | BDI_CAP_MAP_COPY,
+ .unplug_io_fn = default_unplug_io_fn,
+ };
+
+@@ -336,7 +336,7 @@ static struct backing_dev_info rd_backin
+ */
+ static struct backing_dev_info rd_file_backing_dev_info = {
+ .ra_pages = 0, /* No readahead */
+- .memory_backed = 0, /* Does contribute to dirty memory */
++ .capabilities = BDI_CAP_MAP_COPY, /* Does contribute to dirty memory */
+ .unplug_io_fn = default_unplug_io_fn,
+ };
+
+diff -puN drivers/char/mem.c~bdi-provide-backing-device-capability-information drivers/char/mem.c
+--- 25/drivers/char/mem.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/drivers/char/mem.c Tue Mar 8 16:33:20 2005
+@@ -23,6 +23,7 @@
+ #include <linux/devfs_fs_kernel.h>
+ #include <linux/ptrace.h>
+ #include <linux/device.h>
++#include <linux/backing-dev.h>
+
+ #include <asm/uaccess.h>
+ #include <asm/io.h>
+@@ -744,6 +745,10 @@ static struct file_operations zero_fops
+ .mmap = mmap_zero,
+ };
+
++static struct backing_dev_info zero_bdi = {
++ .capabilities = BDI_CAP_MAP_COPY,
++};
++
+ static struct file_operations full_fops = {
+ .llseek = full_lseek,
+ .read = read_full,
+@@ -790,6 +795,7 @@ static int memory_open(struct inode * in
+ break;
+ #endif
+ case 5:
++ filp->f_mapping->backing_dev_info = &zero_bdi;
+ filp->f_op = &zero_fops;
+ break;
+ case 7:
+diff -puN fs/buffer.c~bdi-provide-backing-device-capability-information fs/buffer.c
+--- 25/fs/buffer.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/fs/buffer.c Tue Mar 8 16:33:20 2005
+@@ -878,7 +878,7 @@ int __set_page_dirty_buffers(struct page
+ if (!TestSetPageDirty(page)) {
+ write_lock_irq(&mapping->tree_lock);
+ if (page->mapping) { /* Race with truncate? */
+- if (!mapping->backing_dev_info->memory_backed)
++ if (mapping_cap_account_dirty(mapping))
+ inc_page_state(nr_dirty);
+ radix_tree_tag_set(&mapping->page_tree,
+ page_index(page),
+diff -puN fs/fs-writeback.c~bdi-provide-backing-device-capability-information fs/fs-writeback.c
+--- 25/fs/fs-writeback.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/fs/fs-writeback.c Tue Mar 8 16:33:20 2005
+@@ -315,7 +315,7 @@ sync_sb_inodes(struct super_block *sb, s
+ struct backing_dev_info *bdi = mapping->backing_dev_info;
+ long pages_skipped;
+
+- if (bdi->memory_backed) {
++ if (!bdi_cap_writeback_dirty(bdi)) {
+ list_move(&inode->i_list, &sb->s_dirty);
+ if (sb == blockdev_superblock) {
+ /*
+@@ -566,7 +566,7 @@ int write_inode_now(struct inode *inode,
+ .sync_mode = WB_SYNC_ALL,
+ };
+
+- if (inode->i_mapping->backing_dev_info->memory_backed)
++ if (!mapping_cap_writeback_dirty(inode->i_mapping))
+ return 0;
+
+ might_sleep();
+diff -puN fs/hugetlbfs/inode.c~bdi-provide-backing-device-capability-information fs/hugetlbfs/inode.c
+--- 25/fs/hugetlbfs/inode.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/fs/hugetlbfs/inode.c Tue Mar 8 16:33:20 2005
+@@ -40,7 +40,7 @@ static struct inode_operations hugetlbfs
+
+ static struct backing_dev_info hugetlbfs_backing_dev_info = {
+ .ra_pages = 0, /* No readahead */
+- .memory_backed = 1, /* Does not contribute to dirty memory */
++ .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+ };
+
+ int sysctl_hugetlb_shm_group;
+diff -puN fs/ramfs/inode.c~bdi-provide-backing-device-capability-information fs/ramfs/inode.c
+--- 25/fs/ramfs/inode.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/fs/ramfs/inode.c Tue Mar 8 16:33:20 2005
+@@ -45,7 +45,9 @@ static struct inode_operations ramfs_dir
+
+ static struct backing_dev_info ramfs_backing_dev_info = {
+ .ra_pages = 0, /* No readahead */
+- .memory_backed = 1, /* Does not contribute to dirty memory */
++ .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK |
++ BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY |
++ BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP,
+ };
+
+ struct inode *ramfs_get_inode(struct super_block *sb, int mode, dev_t dev)
+diff -puN fs/sysfs/inode.c~bdi-provide-backing-device-capability-information fs/sysfs/inode.c
+--- 25/fs/sysfs/inode.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/fs/sysfs/inode.c Tue Mar 8 16:33:20 2005
+@@ -23,7 +23,7 @@ static struct address_space_operations s
+
+ static struct backing_dev_info sysfs_backing_dev_info = {
+ .ra_pages = 0, /* No readahead */
+- .memory_backed = 1, /* Does not contribute to dirty memory */
++ .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+ };
+
+ struct inode * sysfs_new_inode(mode_t mode)
+diff -puN include/linux/backing-dev.h~bdi-provide-backing-device-capability-information include/linux/backing-dev.h
+--- 25/include/linux/backing-dev.h~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/include/linux/backing-dev.h Tue Mar 8 16:33:20 2005
+@@ -25,13 +25,39 @@ typedef int (congested_fn)(void *, int);
+ struct backing_dev_info {
+ unsigned long ra_pages; /* max readahead in PAGE_CACHE_SIZE units */
+ unsigned long state; /* Always use atomic bitops on this */
+- int memory_backed; /* Cannot clean pages with writepage */
++ unsigned int capabilities; /* Device capabilities */
+ congested_fn *congested_fn; /* Function pointer if device is md/dm */
+ void *congested_data; /* Pointer to aux data for congested func */
+ void (*unplug_io_fn)(struct backing_dev_info *, struct page *);
+ void *unplug_io_data;
+ };
+
++
++/*
++ * Flags in backing_dev_info::capability
++ * - The first two flags control whether dirty pages will contribute to the
++ * VM's accounting and whether writepages() should be called for dirty pages
++ * (something that would not, for example, be appropriate for ramfs)
++ * - These flags let !MMU mmap() govern direct device mapping vs immediate
++ * copying more easily for MAP_PRIVATE, especially for ROM filesystems
++ */
++#define BDI_CAP_NO_ACCT_DIRTY 0x00000001 /* Dirty pages shouldn't contribute to accounting */
++#define BDI_CAP_NO_WRITEBACK 0x00000002 /* Don't write pages back */
++#define BDI_CAP_MAP_COPY 0x00000004 /* Copy can be mapped (MAP_PRIVATE) */
++#define BDI_CAP_MAP_DIRECT 0x00000008 /* Can be mapped directly (MAP_SHARED) */
++#define BDI_CAP_READ_MAP 0x00000010 /* Can be mapped for reading */
++#define BDI_CAP_WRITE_MAP 0x00000020 /* Can be mapped for writing */
++#define BDI_CAP_EXEC_MAP 0x00000040 /* Can be mapped for execution */
++#define BDI_CAP_VMFLAGS \
++ (BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP)
++
++#if defined(VM_MAYREAD) && \
++ (BDI_CAP_READ_MAP != VM_MAYREAD || \
++ BDI_CAP_WRITE_MAP != VM_MAYWRITE || \
++ BDI_CAP_EXEC_MAP != VM_MAYEXEC)
++#error please change backing_dev_info::capabilities flags
++#endif
++
+ extern struct backing_dev_info default_backing_dev_info;
+ void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page);
+
+@@ -62,4 +88,17 @@ static inline int bdi_rw_congested(struc
+ (1 << BDI_write_congested));
+ }
+
++#define bdi_cap_writeback_dirty(bdi) \
++ (!((bdi)->capabilities & BDI_CAP_NO_WRITEBACK))
++
++#define bdi_cap_account_dirty(bdi) \
++ (!((bdi)->capabilities & BDI_CAP_NO_ACCT_DIRTY))
++
++#define mapping_cap_writeback_dirty(mapping) \
++ bdi_cap_writeback_dirty((mapping)->backing_dev_info)
++
++#define mapping_cap_account_dirty(mapping) \
++ bdi_cap_account_dirty((mapping)->backing_dev_info)
++
++
+ #endif /* _LINUX_BACKING_DEV_H */
+diff -puN mm/filemap.c~bdi-provide-backing-device-capability-information mm/filemap.c
+--- 25/mm/filemap.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/mm/filemap.c Tue Mar 8 16:33:20 2005
+@@ -172,7 +172,7 @@ static int __filemap_fdatawrite_range(st
+ .end = end,
+ };
+
+- if (mapping->backing_dev_info->memory_backed)
++ if (!mapping_cap_writeback_dirty(mapping))
+ return 0;
+
+ ret = do_writepages(mapping, &wbc);
+@@ -269,7 +269,7 @@ int sync_page_range(struct inode *inode,
+ pgoff_t end = (pos + count - 1) >> PAGE_CACHE_SHIFT;
+ int ret;
+
+- if (mapping->backing_dev_info->memory_backed || !count)
++ if (!mapping_cap_writeback_dirty(mapping) || !count)
+ return 0;
+ ret = filemap_fdatawrite_range(mapping, pos, pos + count - 1);
+ if (ret == 0) {
+@@ -295,7 +295,7 @@ int sync_page_range_nolock(struct inode
+ pgoff_t end = (pos + count - 1) >> PAGE_CACHE_SHIFT;
+ int ret;
+
+- if (mapping->backing_dev_info->memory_backed || !count)
++ if (!mapping_cap_writeback_dirty(mapping) || !count)
+ return 0;
+ ret = filemap_fdatawrite_range(mapping, pos, pos + count - 1);
+ if (ret == 0)
+diff -puN mm/page-writeback.c~bdi-provide-backing-device-capability-information mm/page-writeback.c
+--- 25/mm/page-writeback.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/mm/page-writeback.c Tue Mar 8 16:33:53 2005
+@@ -627,7 +627,7 @@ int __set_page_dirty_nobuffers(struct pa
+ mapping2 = page_mapping(page);
+ if (mapping2) { /* Race with truncate? */
+ BUG_ON(mapping2 != mapping);
+- if (!mapping->backing_dev_info->memory_backed)
++ if (mapping_cap_account_dirty(mapping))
+ inc_page_state(nr_dirty);
+ radix_tree_tag_set(&mapping->page_tree,
+ page_index(page), PAGECACHE_TAG_DIRTY);
+@@ -713,7 +713,7 @@ int test_clear_page_dirty(struct page *p
+ page_index(page),
+ PAGECACHE_TAG_DIRTY);
+ write_unlock_irqrestore(&mapping->tree_lock, flags);
+- if (!mapping->backing_dev_info->memory_backed)
++ if (mapping_cap_account_dirty(mapping))
+ dec_page_state(nr_dirty);
+ return 1;
+ }
+@@ -744,7 +744,7 @@ int clear_page_dirty_for_io(struct page
+
+ if (mapping) {
+ if (TestClearPageDirty(page)) {
+- if (!mapping->backing_dev_info->memory_backed)
++ if (mapping_cap_account_dirty(mapping))
+ dec_page_state(nr_dirty);
+ return 1;
+ }
+diff -puN mm/readahead.c~bdi-provide-backing-device-capability-information mm/readahead.c
+--- 25/mm/readahead.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/mm/readahead.c Tue Mar 8 16:33:20 2005
+@@ -23,6 +23,7 @@ EXPORT_SYMBOL(default_unplug_io_fn);
+ struct backing_dev_info default_backing_dev_info = {
+ .ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE,
+ .state = 0,
++ .capabilities = BDI_CAP_MAP_COPY,
+ .unplug_io_fn = default_unplug_io_fn,
+ };
+ EXPORT_SYMBOL_GPL(default_backing_dev_info);
+diff -puN mm/shmem.c~bdi-provide-backing-device-capability-information mm/shmem.c
+--- 25/mm/shmem.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/mm/shmem.c Tue Mar 8 16:33:20 2005
+@@ -184,8 +184,8 @@ static struct vm_operations_struct shmem
+
+ static struct backing_dev_info shmem_backing_dev_info = {
+ .ra_pages = 0, /* No readahead */
+- .memory_backed = 1, /* Does not contribute to dirty memory */
+- .unplug_io_fn = default_unplug_io_fn,
++ .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
++ .unplug_io_fn = default_unplug_io_fn,
+ };
+
+ static LIST_HEAD(shmem_swaplist);
+diff -puN mm/swap_state.c~bdi-provide-backing-device-capability-information mm/swap_state.c
+--- 25/mm/swap_state.c~bdi-provide-backing-device-capability-information Tue Mar 8 16:33:20 2005
++++ 25-akpm/mm/swap_state.c Tue Mar 8 16:33:20 2005
+@@ -29,7 +29,7 @@ static struct address_space_operations s
+ };
+
+ static struct backing_dev_info swap_backing_dev_info = {
+- .memory_backed = 1, /* Does not contribute to dirty memory */
++ .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+ .unplug_io_fn = swap_unplug_io_fn,
+ };
+
+_
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