Re: kmem_alloc() issues

[Steve Lord <lord@sgi.com>]

On Fri, 2002-03-08 at 16:54, Mr. Fiddlehead wrote:
> file: fs/xfs_support/kmem.c
> 
> When kmem_alloc() fails to get a kmalloc() within
> DEF_PRIORITY retries it will alloc the memory from
> __vmalloc() which will cause an Oops when the memory
> is kmem_free()'d if the size is <= MAX_SLAB_SIZE.

I think this will fix that problem:
*** 155,164 ****
  void
  kmem_free(void *ptr, size_t size)
  {
!       if (MAX_SLAB_SIZE < size){
!               vfree(ptr);
!       } else {
                kfree(ptr);
        }
  }
  
--- 155,165 ----
  void
  kmem_free(void *ptr, size_t size)
  {
!       struct page     *p = virt_to_page(ptr);
!       if (VALID_PAGE(p) && PageSlab(p)) {
                kfree(ptr);
+       } else {
+               vfree(ptr);
        }
  }
  
> 
> Further, just before the panic, the line should read,
> 
> if (!rval && (flags & KM_SLEEP))
>    panic()
> 
> but would that be more proper as,
> 
> if (!rval && (flags & (KM_SLEEP | KM_SLEEP_IO))
>    panic()


KM_SLEEP_IO is gone in recent kernels.

> 
> Note that lowering MAX_SLAB_SIZE to 64K from 128K
> helps alleviate this problem, as well as putting in a
> retry instead of the panic().  On linux 2.4.16 I'm
> seeing this on a system with 512MB of RAM on an SMP
> system with 1.7TB of attached storage (LSI raid 5 via
> software raid 0).  This helps to alleviate the
> pressure on the bigger slabs (size-64 and size-128). 
> I tried lowering it to 32K but this bombed on boot
> when the aic7xxx was initialised.

I will try this here for a while.

> 
> I've also inserted a
> wake_up_interruptible(&kswapd_wait) here before
> resetting shrink to 24 (instead of 6) and repeating. 
> I've seen the system retry up to about 48 times, which
> is bad, but not as bad as a panic.

hmm, there might be better things to do than this, possibly
calling free_more_memory().


> 
> This appears to be a problem with the page cache not
> releasing pages for use by the slab cache (kmalloc),
> since I still have about 450MB of inactive page cache
> available when this happens.
> 
> This could also happen under VERY severe conditions in
> kmem_zone_alloc() and kmem_zone_zalloc() but it is
> very unlikely I suspect.
> 
> Cheers!
> 
> Mr F.

Thanks,

  Steve

> 
> 
-- 

Steve Lord                                      voice: +1-651-683-3511
Principal Engineer, Filesystem Software         email: lord@sgi.com