Chuck Ebbert <[email protected]> wrote:
>
> Chris Largret is getting repeated OOM kills because of DMA memory
> exhaustion:
>
> oom-killer: gfp_mask=0xd1, order=3
>
This could be related to the known GFP_DMA oom on some x86_64 machines.
> Looking at floppy_open, we have:
>
> if (!floppy_track_buffer) {
> /* if opening an ED drive, reserve a big buffer,
> * else reserve a small one */
> if ((UDP->cmos == 6) || (UDP->cmos == 5))
> try = 64; /* Only 48 actually useful */
> else
> try = 32; /* Only 24 actually useful */
>
> tmp = (char *)fd_dma_mem_alloc(1024 * try);
> if (!tmp && !floppy_track_buffer) {
> try >>= 1; /* buffer only one side */
> INFBOUND(try, 16);
> tmp = (char *)fd_dma_mem_alloc(1024 * try);
> }
> if (!tmp && !floppy_track_buffer) {
> fallback_on_nodma_alloc(&tmp, 2048 * try);
> }
>
> So it will try to allocate half its first request if that fails, then
> fall back to non-DMA memory as a last resort, but doesn't get a chance
> because the OOM killer gets invoked. Maybe we need a new flag that says
> "fail me immediately if no memory available"?
That's __GFP_NORETRY.
> Or should floppy.c be fixed so it doesn't ask for so much?
>
The page allocator uses 32k as the threshold for when-to-try-like-crazy.
x86_64 should probably be defining its own fd_dma_mem_alloc() which doesn't
use GFP_DMA.
--- devel/drivers/block/floppy.c~floppy-false-oom-fix 2006-02-26 10:14:38.000000000 -0800
+++ devel-akpm/drivers/block/floppy.c 2006-02-26 10:15:04.000000000 -0800
@@ -278,7 +278,8 @@ static void do_fd_request(request_queue_
#endif
#ifndef fd_dma_mem_alloc
-#define fd_dma_mem_alloc(size) __get_dma_pages(GFP_KERNEL,get_order(size))
+#define fd_dma_mem_alloc(size) \
+ __get_dma_pages(GFP_KERNEL|__GFP_NORETRY,get_order(size))
#endif
static inline void fallback_on_nodma_alloc(char **addr, size_t l)
_
-
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