@@ -205,6 +205,18 @@ struct vm_operations_struct {
* writable, if an error is returned it will cause a SIGBUS */
int (*page_mkwrite)(struct vm_area_struct *vma, struct vm_fault *vmf);
+ /* request to make future writes to this page fast. only called
+ * on shared writable maps. return 0 on success (or if there's
+ * nothing to do).
+ *
+ * return the number of bytes for which the operation worked (i.e.
+ * zero if unsupported) or a negative error if something goes wrong.
+ *
+ * called with mmap_sem held for read.
+ */
+ long (*willwrite)(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end);
+
/* called by access_process_vm when get_user_pages() fails, typically
* for use by special VMAs that can switch between memory and hardware
*/
@@ -52,6 +52,9 @@
overrides the coredump filter bits */
#define MADV_DODUMP 17 /* Clear the MADV_NODUMP flag */
+#define MADV_WILLWRITE 18 /* Will write to this page, but maybe
+ only after a while */
+
/* compatibility flags */
#define MAP_FILE 0
@@ -31,6 +31,7 @@ static int madvise_need_mmap_write(int behavior)
case MADV_REMOVE:
case MADV_WILLNEED:
case MADV_DONTNEED:
+ case MADV_WILLWRITE:
return 0;
default:
/* be safe, default to 1. list exceptions explicitly */
@@ -337,6 +338,24 @@ static long madvise_remove(struct vm_area_struct *vma,
return error;
}
+static long madvise_willwrite(struct vm_area_struct * vma,
+ struct vm_area_struct ** prev,
+ unsigned long start, unsigned long end)
+{
+ *prev = vma;
+
+ if (!(vma->vm_flags & VM_WRITE))
+ return -EFAULT;
+
+ if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
+ return 0; /* Not yet supported */
+
+ if (!vma->vm_file || !vma->vm_ops || !vma->vm_ops->willwrite)
+ return 0; /* Not supported */
+
+ return vma->vm_ops->willwrite(vma, start, end);
+}
+
#ifdef CONFIG_MEMORY_FAILURE
/*
* Error injection support for memory error handling.
@@ -380,6 +399,8 @@ madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
return madvise_willneed(vma, prev, start, end);
case MADV_DONTNEED:
return madvise_dontneed(vma, prev, start, end);
+ case MADV_WILLWRITE:
+ return madvise_willwrite(vma, prev, start, end);
default:
return madvise_behavior(vma, prev, start, end, behavior);
}
@@ -407,6 +428,7 @@ madvise_behavior_valid(int behavior)
#endif
case MADV_DONTDUMP:
case MADV_DODUMP:
+ case MADV_WILLWRITE:
return 1;
default:
@@ -465,6 +487,7 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
int write;
size_t len;
struct blk_plug plug;
+ long sum_rets = 0;
#ifdef CONFIG_MEMORY_FAILURE
if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
@@ -526,8 +549,9 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
/* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
error = madvise_vma(vma, &prev, start, tmp, behavior);
- if (error)
+ if (error < 0)
goto out;
+ sum_rets += error;
start = tmp;
if (prev && start < prev->vm_end)
start = prev->vm_end;
@@ -546,5 +570,5 @@ out:
else
up_read(¤t->mm->mmap_sem);
- return error;
+ return error ? error : sum_rets;
}
This should not cause data to be written to disk. It should, however, do any expensive operations that would otherwise happen on the first write fault to this range. Some day this may COW private mappings, allocate real memory instead of zero pages, etc. For now it just passes the request down to filesystems on shared writable mappings. Signed-off-by: Andy Lutomirski <luto@amacapital.net> --- include/linux/mm.h | 12 ++++++++++++ include/uapi/asm-generic/mman-common.h | 3 +++ mm/madvise.c | 28 ++++++++++++++++++++++++++-- 3 files changed, 41 insertions(+), 2 deletions(-)