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Subject[RFC][PATCH] __GFP_FAIL (was: Re: [PATCH] fork() failing)
On Thu, 18 Oct 2001, Marcelo Tosatti wrote:
> On Thu, 18 Oct 2001, Rik van Riel wrote:

> > We just need to make sure that the "wake up kswapd and maybe
> > help free memory" point is EXACTLY the same as the __GFP_FAIL
> > failure point.
>
> Ok, great, that works fine. We can do that for 2.4, no problem.

A quick (untested) patch to demonstrate my idea is below
my signature. Note the comments in __alloc_pages() ...
it's important to only fail our __GFP_FAIL allocation
_after_ having woken up kswapd.

regards,

Rik
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--- linux-2.4.12-ac3/mm/page_alloc.c.nofail Thu Oct 18 23:24:50 2001
+++ linux-2.4.12-ac3/mm/page_alloc.c Fri Oct 19 01:34:31 2001
@@ -341,18 +341,25 @@

/*
* OK, none of the zones on our zonelist has lots
- * of pages free.
- *
- * We wake up kswapd, in the hope that kswapd will
- * resolve this situation before memory gets tight.
- *
- * We'll also help a bit trying to free pages, this
- * way statistics will make sure really fast allocators
- * are slowed down more than slow allocators and other
- * programs in the system shouldn't be impacted as much
- * by the hogs.
+ * of pages free. Kswapd has work to do ...
*/
wakeup_kswapd();
+
+ /*
+ * We don't want to do memory balancing work ourself,
+ * instead we fail this allocation and hope that kswapd
+ * will have things in a better shape next time.
+ */
+ if (gfp_mask & __GFP_FAIL)
+ return NULL;
+
+ /*
+ * Free some pages ourselves, rather than eating up the
+ * last few free pages and running the system into the
+ * ground. Since this slows down heavy allocators more
+ * than occasional allocators, it provides some fairness
+ * and smoother behaviour under heavy load.
+ */
if ((gfp_mask & __GFP_WAIT) && !(current->flags & PF_MEMALLOC))
try_to_free_pages(gfp_mask);

--- linux-2.4.12-ac3/include/linux/mm.h.nofail Fri Oct 19 01:29:19 2001
+++ linux-2.4.12-ac3/include/linux/mm.h Fri Oct 19 01:33:30 2001
@@ -567,12 +567,14 @@
#define __GFP_HIGH 0x20 /* Should access emergency pools? */
#define __GFP_IO 0x40 /* Can start physical IO? */
#define __GFP_FS 0x80 /* Can call down to low-level FS? */
+#define __GFP_FAIL 0x100 /* Fail early when low on free pages. */

#define GFP_NOIO (__GFP_HIGH | __GFP_WAIT)
#define GFP_NOFS (__GFP_HIGH | __GFP_WAIT | __GFP_IO)
#define GFP_ATOMIC (__GFP_HIGH)
#define GFP_USER ( __GFP_WAIT | __GFP_IO | __GFP_FS)
#define GFP_HIGHUSER ( __GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_HIGHMEM)
+#define GFP_READAHEAD ( __GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_HIGHMEM | __GFP_FAIL)
#define GFP_KERNEL (__GFP_HIGH | __GFP_WAIT | __GFP_IO | __GFP_FS)
#define GFP_NFS (__GFP_HIGH | __GFP_WAIT | __GFP_IO | __GFP_FS)
#define GFP_KSWAPD ( __GFP_IO | __GFP_FS)
-
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