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SubjectRe: [RFC][PATCH 4/5] PM/Hibernate: Rework shrinking of memory
Date
On Thursday 07 May 2009, Nigel Cunningham wrote:
> Hi.

Hi,

> On Thu, 2009-05-07 at 00:44 +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rjw@sisk.pl>
> >
> > Rework swsusp_shrink_memory() so that it calls shrink_all_memory()
> > just once to make some room for the image and then allocates memory
> > to apply more pressure to the memory management subsystem, if
> > necessary.
> >
> > Unfortunately, we don't seem to be able to drop shrink_all_memory()
> > entirely just yet, because that would lead to huge performance
> > regressions in some test cases.
>
> I know it doesn't fit with your current way of doing things, but have
> you considered trying larger order allocations as a means of getting
> memory freed?

Actually, I was thinking about that. What's your experience with this
approach?

> I have code in tuxonice_prepare_image.c (look for extra_pages_allocated) that
> might be helpful for this purpose.

OK, thanks. I'll have a look at it.

> > Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
> > ---
> > kernel/power/snapshot.c | 145 ++++++++++++++++++++++++++++++++----------------
> > 1 file changed, 98 insertions(+), 47 deletions(-)
> >
> > Index: linux-2.6/kernel/power/snapshot.c
> > ===================================================================
> > --- linux-2.6.orig/kernel/power/snapshot.c
> > +++ linux-2.6/kernel/power/snapshot.c
> > @@ -1066,69 +1066,120 @@ void swsusp_free(void)
> > buffer = NULL;
> > }
> >
> > +/* Helper functions used for the shrinking of memory. */
> > +
> > /**
> > - * swsusp_shrink_memory - Try to free as much memory as needed
> > - *
> > - * ... but do not OOM-kill anyone
> > + * preallocate_image_memory - Allocate given number of page frames
> > + * @nr_pages: Number of page frames to allocate
> > *
> > - * Notice: all userland should be stopped before it is called, or
> > - * livelock is possible.
> > + * Return value: Number of page frames actually allocated
> > */
> > -
> > -#define SHRINK_BITE 10000
> > -static inline unsigned long __shrink_memory(long tmp)
> > +static unsigned long preallocate_image_memory(unsigned long nr_pages)
> > {
> > - if (tmp > SHRINK_BITE)
> > - tmp = SHRINK_BITE;
> > - return shrink_all_memory(tmp);
> > + unsigned long nr_alloc = 0;
> > +
> > + while (nr_pages-- > 0) {
> > + struct page *page;
> > +
> > + page = alloc_image_page(GFP_KERNEL | __GFP_NOWARN);
>
> Ah... now I see you're using __GFP_NOWARN already :)
>
> > + if (!page)
> > + break;
> > + nr_alloc++;
> > + }
> > +
> > + return nr_alloc;
> > }
> >
> > +/**
> > + * swsusp_shrink_memory - Make the kernel release as much memory as needed
> > + *
> > + * To create a hibernation image it is necessary to make a copy of every page
> > + * frame in use. We also need a number of page frames to be free during
> > + * hibernation for allocations made while saving the image and for device
> > + * drivers, in case they need to allocate memory from their hibernation
> > + * callbacks (these two numbers are given by PAGES_FOR_IO and SPARE_PAGES,
> > + * respectively, both of which are rough estimates). To make this happen, we
> > + * compute the total number of available page frames and allocate at least
> > + *
> > + * ([page frames total] + PAGES_FOR_IO + [metadata pages]) / 2 + 2 * SPARE_PAGES
> > + *
> > + * of them, which corresponds to the maximum size of a hibernation image.
> > + *
> > + * If image_size is set below the number following from the above formula,
> > + * the preallocation of memory is continued until the total number of page
> > + * frames in use is below the requested image size or it is impossible to
> > + * allocate more memory, whichever happens first.
> > + */
>
> You should also be taking into account how much storage is available
> here - that would make things more reliable. If compression is begin
> used, you could also apply an 'expected compression ratio' so that you
> don't unnecessarily free memory that will fit once compressed.

Currently compression is only done in user space so I don't know in advance
whether or not it's going to be used.

> > int swsusp_shrink_memory(void)
> > {
> > - long tmp;
> > struct zone *zone;
> > - unsigned long pages = 0;
> > - unsigned int i = 0;
> > - char *p = "-\\|/";
> > + unsigned long saveable, size, max_size, count, pages = 0;
> > struct timeval start, stop;
> > + int error = 0;
> >
> > - printk(KERN_INFO "PM: Shrinking memory... ");
> > + printk(KERN_INFO "PM: Shrinking memory ... ");
>
> Without the space is normal, at least to my mind.

OK

> > do_gettimeofday(&start);
> > - do {
> > - long size, highmem_size;
> >
> > - highmem_size = count_highmem_pages();
> > - size = count_data_pages() + PAGES_FOR_IO + SPARE_PAGES;
> > - tmp = size;
> > - size += highmem_size;
> > - for_each_populated_zone(zone) {
> > - tmp += snapshot_additional_pages(zone);
> > - if (is_highmem(zone)) {
> > - highmem_size -=
> > - zone_page_state(zone, NR_FREE_PAGES);
> > - } else {
> > - tmp -= zone_page_state(zone, NR_FREE_PAGES);
> > - tmp += zone->lowmem_reserve[ZONE_NORMAL];
> > - }
> > - }
> > + /* Count the number of saveable data pages. */
> > + saveable = count_data_pages() + count_highmem_pages();
> > +
> > + /*
> > + * Compute the total number of page frames we can use (count) and the
> > + * number of pages needed for image metadata (size).
> > + */
> > + count = saveable;
> > + size = 0;
> > + for_each_populated_zone(zone) {
> > + size += snapshot_additional_pages(zone);
> > + count += zone_page_state(zone, NR_FREE_PAGES);
> > + if (!is_highmem(zone))
> > + count -= zone->lowmem_reserve[ZONE_NORMAL];
> > + }
> >
> > - if (highmem_size < 0)
> > - highmem_size = 0;
>
> You're not taking watermarks into account here - that isn't a problem
> with shrink_all_memory because it usually frees more than you ask for
> (or has done in the past), but if you're getting exactly what you ask
> for, you might run into trouble if more than half of memory is in use to
> start with.

Hmm, why exactly?

> > + /* Compute the maximum number of saveable pages to leave in memory. */
> > + max_size = (count - (size + PAGES_FOR_IO)) / 2 - 2 * SPARE_PAGES;
> > + size = DIV_ROUND_UP(image_size, PAGE_SIZE);
> > + if (size > max_size)
> > + size = max_size;
> > + /*
> > + * If the maximum is not lesser than the current number of saveable
>
> s/lesser/less/

Right, thanks.

> > + * pages in memory, we don't need to do anything more.
> > + */
> > + if (size >= saveable)
> > + goto out;
> >
> > - tmp += highmem_size;
> > - if (tmp > 0) {
> > - tmp = __shrink_memory(tmp);
> > - if (!tmp)
> > - return -ENOMEM;
> > - pages += tmp;
> > - } else if (size > image_size / PAGE_SIZE) {
> > - tmp = __shrink_memory(size - (image_size / PAGE_SIZE));
> > - pages += tmp;
> > - }
> > - printk("\b%c", p[i++%4]);
> > - } while (tmp > 0);
> > + /*
> > + * Let the memory management subsystem know that we're going to need a
> > + * large number of page frames to allocate and make it free some memory.
> > + * NOTE: If this is not done, performance is heavily affected in some
> > + * test cases.
> > + */
> > + shrink_all_memory(saveable - size);
> > +
> > + /*
> > + * The number of saveable pages in memory was too high, so apply some
> > + * pressure to decrease it. First, make room for the largest possible
> > + * image and fail if that doesn't work. Next, try to decrease the size
> > + * of the image as much as indicated by image_size.
> > + */
> > + count -= max_size;
> > + pages = preallocate_image_memory(count);
> > + if (pages < count)
> > + error = -ENOMEM;
> > + else
> > + pages += preallocate_image_memory(max_size - size);
> > +
> > + /* Release all of the preallocated page frames. */
> > + swsusp_free();
> > +
> > + if (error) {
> > + printk(KERN_CONT "\n");
> > + return error;
> > + }
> > +
> > + out:
> > do_gettimeofday(&stop);
> > - printk("\bdone (%lu pages freed)\n", pages);
> > + printk(KERN_CONT "done (preallocated %lu free pages)\n", pages);
> > swsusp_show_speed(&start, &stop, pages, "Freed");
> >
> > return 0;

Best,
Rafael


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