proc: less memory for /proc/*/map_files readdir

dentry name can be evaluated later, right before calling into VFS.

Also, spend less time under ->mmap_sem.

Link: http://lkml.kernel.org/r/20171110163034.GA2534@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 4c12cb2..a3efc24 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2026,9 +2026,9 @@ out:
 }
 
 struct map_files_info {
+       unsigned long   start;
+       unsigned long   end;
        fmode_t         mode;
-       unsigned int    len;
-       unsigned char   name[4*sizeof(long)+2]; /* max: %lx-%lx\0 */
 };
 
 /*
@@ -2198,10 +2198,9 @@ proc_map_files_readdir(struct file *file, struct dir_context *ctx)
                        if (++pos <= ctx->pos)
                                continue;
 
+                       info.start = vma->vm_start;
+                       info.end = vma->vm_end;
                        info.mode = vma->vm_file->f_mode;
-                       info.len = snprintf(info.name,
-                                       sizeof(info.name), "%lx-%lx",
-                                       vma->vm_start, vma->vm_end);
                        if (flex_array_put(fa, i++, &info, GFP_KERNEL))
                                BUG();
                }
@@ -2209,9 +2208,13 @@ proc_map_files_readdir(struct file *file, struct dir_context *ctx)
        up_read(&mm->mmap_sem);
 
        for (i = 0; i < nr_files; i++) {
+               char buf[4 * sizeof(long) + 2]; /* max: %lx-%lx\0 */
+               unsigned int len;
+
                p = flex_array_get(fa, i);
+               len = snprintf(buf, sizeof(buf), "%lx-%lx", p->start, p->end);
                if (!proc_fill_cache(file, ctx,
-                                     p->name, p->len,
+                                     buf, len,
                                      proc_map_files_instantiate,
                                      task,
                                      (void *)(unsigned long)p->mode))