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SubjectRe: Linux 2.6.7-rc2
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Linus Torvalds <torvalds@osdl.org> writes:

> On Mon, 31 May 2004, Peter Osterlund wrote:
> >
> > If I put "#if 0" around the *wdata assignment in nfs_writepage_sync,
> > the stack usage goes down to 36, so it looks like gcc is building a
> > temporary structure on the stack and then copies the whole thing to
> > *wdata.
>
> Yeah, that's silly. But understandable. A lot of problems go away by doing
> a temporary private node..
>
> > Does this construct save stack space for any version of gcc? Maybe the
> > code should be changed to do a memset() followed by explicit
> > initialization of the non-zero member variables instead.
>
> In this case, I'd agree.
>
> In some other cases, it's better to create a initialized static variable,
> and just use that as an initial initializer. In this case that doesn't
> much help, since none of the fields are constant.

Here is a patch that does this. I've verified that it compiles and
that it fixes the excessive stack problem, but I failed to come up
with a test case that exercises these code paths.


--- linux/fs/nfs/read.c.orig 2004-05-31 23:34:15.890307512 +0200
+++ linux/fs/nfs/read.c 2004-05-31 23:29:26.077365776 +0200
@@ -103,22 +103,16 @@
if (!rdata)
return -ENOMEM;

- *rdata = (struct nfs_read_data) {
- .flags = (IS_SWAPFILE(inode)? NFS_RPC_SWAPFLAGS : 0),
- .cred = NULL,
- .inode = inode,
- .pages = LIST_HEAD_INIT(rdata->pages),
- .args = {
- .fh = NFS_FH(inode),
- .lockowner = current->files,
- .pages = &page,
- .pgbase = 0UL,
- .count = rsize,
- },
- .res = {
- .fattr = &rdata->fattr,
- }
- };
+ memset(rdata, 0, sizeof(*rdata));
+ rdata->flags = (IS_SWAPFILE(inode)? NFS_RPC_SWAPFLAGS : 0);
+ rdata->inode = inode;
+ INIT_LIST_HEAD(&rdata->pages);
+ rdata->args.fh = NFS_FH(inode);
+ rdata->args.lockowner = current->files;
+ rdata->args.pages = &page;
+ rdata->args.pgbase = 0UL;
+ rdata->args.count = rsize;
+ rdata->res.fattr = &rdata->fattr;

dprintk("NFS: nfs_readpage_sync(%p)\n", page);

--- linux/fs/nfs/write.c.orig 2004-05-31 23:34:20.529602232 +0200
+++ linux/fs/nfs/write.c 2004-05-31 23:29:33.165288248 +0200
@@ -185,23 +185,17 @@
if (!wdata)
return -ENOMEM;

- *wdata = (struct nfs_write_data) {
- .flags = how,
- .cred = NULL,
- .inode = inode,
- .args = {
- .fh = NFS_FH(inode),
- .lockowner = current->files,
- .pages = &page,
- .stable = NFS_FILE_SYNC,
- .pgbase = offset,
- .count = wsize,
- },
- .res = {
- .fattr = &wdata->fattr,
- .verf = &wdata->verf,
- },
- };
+ memset(wdata, 0, sizeof(*wdata));
+ wdata->flags = how;
+ wdata->inode = inode;
+ wdata->args.fh = NFS_FH(inode);
+ wdata->args.lockowner = current->files;
+ wdata->args.pages = &page;
+ wdata->args.stable = NFS_FILE_SYNC;
+ wdata->args.pgbase = offset;
+ wdata->args.count = wsize;
+ wdata->res.fattr = &wdata->fattr;
+ wdata->res.verf = &wdata->verf;

dprintk("NFS: nfs_writepage_sync(%s/%Ld %d@%Ld)\n",
inode->i_sb->s_id,
--
Peter Osterlund - petero2@telia.com
http://w1.894.telia.com/~u89404340
-
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