Re: [Bisected Regression in 2.6.35] A full tmpfs filesystem causeshibernation to hang

[Rafael J. Wysocki]

On Friday, September 03, 2010, KOSAKI Motohiro wrote:
> > On Friday, September 03, 2010, KOSAKI Motohiro wrote:
> > > Hello,
> > > 
> > > > > > > Like in the patch below, perhaps?
> > > > > > 
> > > > > > Looks like fine. but I have one question. hibernate_preallocate_memory() call
> > > > > > preallocate_image_memory() two times. Why do you only care latter one?
> > > > > > former one seems similar risk.
> > > > > 
> > > > > The first one is mandatory, ie. if we can't allocate the requested number of
> > > > > pages at this point, we fail the entire hibernation.  In that case the
> > > > > performance hit doesn't matter.
> > > > 
> > > > IOW, your patch at http://lkml.org/lkml/2010/9/2/262 is still necessary to
> > > > protect against the infinite loop in that case.
> > > 
> > > As far as I understand, we need distinguish two allocation failure.
> > >   1) failure because no enough memory
> > > 	-> yes, hibernation should fail
> > >  2) failure because already allocated enough lower zone memory
> > > 	-> why should we fail?
> > > 
> > > If the system has a lot of memory, scenario (2) is happen frequently than (1).
> > > I think we need check alloc_highmem and alloc_normal variable and call
> > > preallocate_image_highmem() again instead preallocate_image_memory()
> > > if we've alread allocated enough lots normal memory.
> > > 
> > > nit?
> > 
> > Actually I thought about that, but we don't really see hibernation fail for
> > this reason.  In all of the tests I carried out the requested 50% of highmem
> > had been allocated before allocations from the normal zone started to be
> > made, even if highmem was 100% full at that point.  So this appears to be
> > a theoretical issue and covering it would require us to change the algorithm
> > entirely (eg. it doesn't make sense to call preallocate_highmem_fraction() down
> > the road if that happens).
> 
> ok, thanks. probably I've catched your point. please feel free to use my reviewed-by
> for your fix.

Thanks.

In the meantime, though, I prepared a patch that should address the issue
entirely.  The patch is appended and if it looks good to you, I'd rather use it
instead of the previous one (it is still untested).

Rafael

---
From: Rafael J. Wysocki <rjw@xxxxxxx>
Subject: PM / Hibernate: Avoid hitting OOM during preallocation of memory

There is a problem in hibernate_preallocate_memory() that it calls
preallocate_image_memory() with an argument that may be greater than
the number of available non-highmem memory pages.  This may trigger
the OOM condition which in turn can cause significant slowdown to
occur.

To avoid that, modify preallocate_image_memory() so that it checks
if there is a sufficient number of non-highmem pages to allocate from
before calling preallocate_image_pages() and change
hibernate_preallocate_memory() to try to allocate from highmem if
the number of pages allocated by preallocate_image_memory() is too
low.

Adjust free_unnecessary_pages() to take all possible memory
allocation patterns into account.

Reported-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
---
 kernel/power/snapshot.c |   66 +++++++++++++++++++++++++++++++++---------------
 1 file changed, 46 insertions(+), 20 deletions(-)

Index: linux-2.6/kernel/power/snapshot.c
===================================================================
--- linux-2.6.orig/kernel/power/snapshot.c
+++ linux-2.6/kernel/power/snapshot.c
@@ -1122,9 +1122,19 @@ static unsigned long preallocate_image_p
 	return nr_alloc;
 }
 
-static unsigned long preallocate_image_memory(unsigned long nr_pages)
+static unsigned long preallocate_image_memory(unsigned long nr_pages,
+					      unsigned long size_normal)
 {
-	return preallocate_image_pages(nr_pages, GFP_IMAGE);
+	unsigned long alloc;
+
+	if (size_normal <= alloc_normal)
+		return 0;
+
+	alloc = size_normal - alloc_normal;
+	if (nr_pages < alloc)
+		alloc = nr_pages;
+
+	return preallocate_image_pages(alloc, GFP_IMAGE);
 }
 
 #ifdef CONFIG_HIGHMEM
@@ -1170,15 +1180,22 @@ static inline unsigned long preallocate_
  */
 static void free_unnecessary_pages(void)
 {
-	unsigned long save_highmem, to_free_normal, to_free_highmem;
+	unsigned long save, to_free_normal, to_free_highmem;
 
-	to_free_normal = alloc_normal - count_data_pages();
-	save_highmem = count_highmem_pages();
-	if (alloc_highmem > save_highmem) {
-		to_free_highmem = alloc_highmem - save_highmem;
+	save = count_data_pages();
+	if (alloc_normal >= save) {
+		to_free_normal = alloc_normal - save;
+		save = 0;
+	} else {
+		to_free_normal = 0;
+		save -= alloc_normal;
+	}
+	save += count_highmem_pages();
+	if (alloc_highmem >= save) {
+		to_free_highmem = alloc_highmem - save;
 	} else {
 		to_free_highmem = 0;
-		to_free_normal -= save_highmem - alloc_highmem;
+		to_free_normal -= save - alloc_highmem;
 	}
 
 	memory_bm_position_reset(&copy_bm);
@@ -1259,7 +1276,7 @@ int hibernate_preallocate_memory(void)
 {
 	struct zone *zone;
 	unsigned long saveable, size, max_size, count, highmem, pages = 0;
-	unsigned long alloc, save_highmem, pages_highmem;
+	unsigned long alloc, save_highmem, pages_highmem, size_normal;
 	struct timeval start, stop;
 	int error;
 
@@ -1296,6 +1313,7 @@ int hibernate_preallocate_memory(void)
 		else
 			count += zone_page_state(zone, NR_FREE_PAGES);
 	}
+	size_normal = count;
 	count += highmem;
 	count -= totalreserve_pages;
 
@@ -1310,7 +1328,7 @@ int hibernate_preallocate_memory(void)
 	 */
 	if (size >= saveable) {
 		pages = preallocate_image_highmem(save_highmem);
-		pages += preallocate_image_memory(saveable - pages);
+		pages += preallocate_image_memory(saveable - pages, size_normal);
 		goto out;
 	}
 
@@ -1336,16 +1354,24 @@ int hibernate_preallocate_memory(void)
 	 */
 	pages_highmem = preallocate_image_highmem(highmem / 2);
 	alloc = (count - max_size) - pages_highmem;
-	pages = preallocate_image_memory(alloc);
-	if (pages < alloc)
-		goto err_out;
-	size = max_size - size;
-	alloc = size;
-	size = preallocate_highmem_fraction(size, highmem, count);
-	pages_highmem += size;
-	alloc -= size;
-	pages += preallocate_image_memory(alloc);
-	pages += pages_highmem;
+	pages = preallocate_image_memory(alloc, size_normal);
+	if (pages < alloc) {
+		/* We have exhausted non-highmem pages, try highmem. */
+		alloc -= pages;
+		pages = preallocate_image_highmem(alloc);
+		if (pages < alloc)
+			goto err_out;
+		pages += preallocate_image_highmem(max_size - size);
+	} else {
+		size = max_size - size;
+		alloc = size;
+		size = preallocate_highmem_fraction(size, highmem, count);
+		pages_highmem += size;
+		alloc -= size;
+		size = preallocate_image_memory(alloc, size_normal);
+		pages_highmem += preallocate_image_highmem(alloc - size);
+		pages += pages_highmem + size;
+	}
 
 	/*
 	 * We only need as many page frames for the image as there are saveable
--
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