On 22.05.2007 [09:16:37 -0500], Steve Fox wrote:
> On Wed, 2007-05-16 at 17:59 -0700, Badari Pulavarty wrote:
>
> > Here it is ..
> >
> > Should I do one for poll() also ?
> >
> > Thanks,
> > Badari
> >
> > Optimize select by a using stack space for small fd sets.
> > core_sys_select() already has this optimization. This is
> > for compat version.
> >
> > Signed-off-by: Badari Pulavarty <[email protected]>
> > ---
> > fs/compat.c | 17 +++++++++++------
> > 1 file changed, 11 insertions(+), 6 deletions(-)
> >
> > Index: linux-2.6.22-rc1/fs/compat.c
> > ===================================================================
> > --- linux-2.6.22-rc1.orig/fs/compat.c 2007-05-12 18:45:56.000000000 -0700
> > +++ linux-2.6.22-rc1/fs/compat.c 2007-05-16 17:50:39.000000000 -0700
> > @@ -1544,9 +1544,10 @@ int compat_core_sys_select(int n, compat
> > compat_ulong_t __user *outp, compat_ulong_t __user *exp, s64 *timeout)
> > {
> > fd_set_bits fds;
> > - char *bits;
> > + void *bits;
> > int size, max_fds, ret = -EINVAL;
> > struct fdtable *fdt;
> > + long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];
> >
> > if (n < 0)
> > goto out_nofds;
> > @@ -1564,11 +1565,14 @@ int compat_core_sys_select(int n, compat
> > * since we used fdset we need to allocate memory in units of
> > * long-words.
> > */
> > - ret = -ENOMEM;
> > size = FDS_BYTES(n);
> > - bits = kmalloc(6 * size, GFP_KERNEL);
> > - if (!bits)
> > - goto out_nofds;
> > + bits = stack_fds;
> > + if (size > sizeof(stack_fds) / 6) {
> > + bits = kmalloc(6 * size, GFP_KERNEL);
> > + ret = -ENOMEM;
> > + if (!bits)
> > + goto out_nofds;
> > + }
> > fds.in = (unsigned long *) bits;
> > fds.out = (unsigned long *) (bits + size);
> > fds.ex = (unsigned long *) (bits + 2*size);
> > @@ -1600,7 +1604,8 @@ int compat_core_sys_select(int n, compat
> > compat_set_fd_set(n, exp, fds.res_ex))
> > ret = -EFAULT;
> > out:
> > - kfree(bits);
> > + if (bits != stack_fds)
> > + kfree(bits);
> > out_nofds:
> > return ret;
> > }
>
> Andy put this through a couple machines on test.kernel.org and elm3b6
> was fixed, however elm3b239 still had a boot error.
>
> BUG: at mm/slab.c:777 __find_general_cachep()
>
> Call Trace:
> [<ffffffff802729c6>] __kmalloc+0xa6/0xe0
> [<ffffffff8021d21b>] cache_k8_northbridges+0x9b/0x120
I believe this is fixed by:
http://lkml.org/lkml/2007/5/18/19
Care to stack it on top and retest?
Thanks,
Nish
--
Nishanth Aravamudan <[email protected]>
IBM Linux Technology Center
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