[PATCH] Shared mmap [Take 3]

Matthew Wilcox
2001-03-12T17:50:42Z

This patch changes shared mmaps of files to always be aligned at the
same offset within the processor's d-cache. This fixes PA-RISC & MIPS.
Sparc & IA-64 need some of their support changing, but I don't want to
do that until everyone's had the chance to disagree with my changes :-)

Index: fs/inode.c
===================================================================
RCS file: /var/cvs/linux/fs/inode.c,v
retrieving revision 1.1.1.3
diff -u -p -r1.1.1.3 inode.c
--- fs/inode.c 2001/01/01 10:32:52 1.1.1.3
+++ fs/inode.c 2001/03/12 13:23:04
@@ -608,6 +608,7 @@ static void clean_inode(struct inode *in
inode->i_data.a_ops = &empty_aops;
inode->i_data.host = inode;
inode->i_mapping = &inode->i_data;
+ inode->i_mmap_offset = -1;
}

/**
Index: include/linux/fs.h
===================================================================
RCS file: /var/cvs/linux/include/linux/fs.h,v
retrieving revision 1.1.1.4
diff -u -p -r1.1.1.4 fs.h
--- include/linux/fs.h 2001/01/01 10:33:09 1.1.1.4
+++ include/linux/fs.h 2001/03/12 13:56:10
@@ -424,6 +424,7 @@ struct inode {

unsigned long i_state;

+ unsigned int i_mmap_offset; /* Handle L1 d-cache aliasing */
unsigned int i_flags;
unsigned char i_sock;

Index: include/linux/mm.h
===================================================================
RCS file: /var/cvs/linux/include/linux/mm.h,v
retrieving revision 1.1.1.4
diff -u -p -r1.1.1.4 mm.h
--- include/linux/mm.h 2001/01/01 10:33:09 1.1.1.4
+++ include/linux/mm.h 2001/03/12 13:56:10
@@ -419,6 +419,7 @@ extern void insert_vm_struct(struct mm_s
extern void __insert_vm_struct(struct mm_struct *, struct vm_area_struct *);
extern void build_mmap_avl(struct mm_struct *);
extern void exit_mmap(struct mm_struct *);
+extern unsigned long get_shared_area(unsigned long, unsigned long, unsigned int);
extern unsigned long get_unmapped_area(unsigned long, unsigned long);

extern unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
Index: mm/mmap.c
===================================================================
RCS file: /var/cvs/linux/mm/mmap.c,v
retrieving revision 1.1.1.4
diff -u -p -r1.1.1.4 mmap.c
--- mm/mmap.c 2001/01/01 10:33:08 1.1.1.4
+++ mm/mmap.c 2001/03/12 16:47:25
@@ -190,6 +190,7 @@ unsigned long do_mmap_pgoff(struct file
{
struct mm_struct * mm = current->mm;
struct vm_area_struct * vma;
+ struct inode *inode = NULL;
int correct_wcount = 0;
int error;

@@ -223,17 +224,18 @@ unsigned long do_mmap_pgoff(struct file
* of the memory object, so we don't do any here.
*/
if (file != NULL) {
+ inode = file->f_dentry->d_inode;
switch (flags & MAP_TYPE) {
case MAP_SHARED:
if ((prot & PROT_WRITE) && !(file->f_mode & FMODE_WRITE))
return -EACCES;

/* Make sure we don't allow writing to an append-only file.. */
- if (IS_APPEND(file->f_dentry->d_inode) && (file->f_mode & FMODE_WRITE))
+ if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
return -EACCES;

/* make sure there are no mandatory locks on the file. */
- if (locks_verify_locked(file->f_dentry->d_inode))
+ if (locks_verify_locked(inode))
return -EAGAIN;

/* fall through */
@@ -253,6 +255,15 @@ unsigned long do_mmap_pgoff(struct file
if (flags & MAP_FIXED) {
if (addr & ~PAGE_MASK)
return -EINVAL;
+ } else if (inode && (flags & MAP_SHARED)) {
+ if (inode->i_mmap_offset != -1) {
+ addr = get_shared_area(addr, len, inode->i_mmap_offset);
+ } else {
+ addr = get_unmapped_area(addr, len);
+ }
+ if (!addr)
+ return -ENOMEM;
+ inode->i_mmap_offset = addr & (SHMLBA - 1);
} else {
addr = get_unmapped_area(addr, len);
if (!addr)
@@ -348,7 +359,7 @@ unsigned long do_mmap_pgoff(struct file

insert_vm_struct(mm, vma);
if (correct_wcount)
- atomic_inc(&file->f_dentry->d_inode->i_writecount);
+ atomic_inc(&inode->i_writecount);

mm->total_vm += len >> PAGE_SHIFT;
if (flags & VM_LOCKED) {
@@ -359,7 +370,7 @@ unsigned long do_mmap_pgoff(struct file

unmap_and_free_vma:
if (correct_wcount)
- atomic_inc(&file->f_dentry->d_inode->i_writecount);
+ atomic_inc(&inode->i_writecount);
vma->vm_file = NULL;
fput(file);
/* Undo any partial mapping done by a device driver. */
@@ -376,6 +387,29 @@ free_vma:
* Return value 0 means ENOMEM.
*/
#ifndef HAVE_ARCH_UNMAPPED_AREA
+
+#define DCACHE_ALIGN(addr) ((addr) &~ (SHMLBA - 1))
+
+unsigned long get_shared_area(unsigned long addr, unsigned long len, unsigned int offset)
+{
+ struct vm_area_struct *vmm;
+
+ if (len > TASK_SIZE)
+ return 0;
+ if (!addr)
+ addr = TASK_UNMAPPED_BASE;
+ addr = DCACHE_ALIGN(addr - offset) + offset;
+
+ for (vmm = find_vma(current->mm, addr); ; vmm = vmm->vm_next) {
+ /* At this point: (!vmm || addr < vmm->vm_end). */
+ if (TASK_SIZE - len < addr)
+ return 0;
+ if (!vmm || addr + len <= vmm->vm_start)
+ return addr;
+ addr = DCACHE_ALIGN(vmm->vm_end - offset) + offset;
+ }
+}
+
unsigned long get_unmapped_area(unsigned long addr, unsigned long len)
{
struct vm_area_struct * vmm;
Index: mm/mremap.c
===================================================================
RCS file: /var/cvs/linux/mm/mremap.c,v
retrieving revision 1.1.1.4
diff -u -p -r1.1.1.4 mremap.c
--- mm/mremap.c 2001/01/01 10:33:09 1.1.1.4
+++ mm/mremap.c 2001/03/11 23:48:55
@@ -276,7 +276,11 @@ unsigned long do_mremap(unsigned long ad
ret = -ENOMEM;
if (flags & MREMAP_MAYMOVE) {
if (!(flags & MREMAP_FIXED)) {
- new_addr = get_unmapped_area(0, new_len);
+ if (vma->vm_file && (vma->vm_flags & VM_SHARED)) {
+ new_addr = get_shared_area(0, new_len, vma->vm_file->f_dentry->d_inode->i_mmap_offset);
+ } else {
+ new_addr = get_unmapped_area(0, new_len);
+ }
if (!new_addr)
goto out;
}

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