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    SubjectRe: [PATCH 5/5] PM/Hibernate: Do not release preallocated memory unnecessarily (rev. 2)
    On Wed, May 06, 2009 at 07:07:44AM +0800, Rafael J. Wysocki wrote:
    > On Tuesday 05 May 2009, Wu Fengguang wrote:
    > > On Tue, May 05, 2009 at 10:24:27AM +0800, Wu Fengguang wrote:
    > > > On Mon, May 04, 2009 at 08:22:38AM +0800, Rafael J. Wysocki wrote:
    > > > > From: Rafael J. Wysocki <rjw@sisk.pl>
    > > > >
    > > > > Since the hibernation code is now going to use allocations of memory
    > > > > to create enough room for the image, it can also use the page frames
    > > > > allocated at this stage as image page frames. The low-level
    > > > > hibernation code needs to be rearranged for this purpose, but it
    > > > > allows us to avoid freeing a great number of pages and allocating
    > > > > these same pages once again later, so it generally is worth doing.
    > > > >
    > > > > [rev. 2: Change the strategy of preallocating memory to allocate as
    > > > > many pages as needed to get the right image size in one shot (the
    > > > > excessive allocated pages are released afterwards).]
    > > >
    > > > Rafael, I tried out your patches and found doubled memory shrink speed!
    > > >
    > > > [ 579.641781] PM: Preallocating image memory ... done (allocated 383900 pages, 128000 image pages kept)
    > > > [ 583.087875] PM: Allocated 1535600 kbytes in 3.43 seconds (447.69 MB/s)
    > >
    > > > For you reference, here is the free memory before/after
    > > > hibernate_preallocate_memory():
    > > >
    > > > # free
    > > > total used free shared buffers cached
    > > > Mem: 1933 1917 15 0 0 1845
    > > > -/+ buffers/cache: 72 1861
    > > > Swap: 0 0 0
    > > >
    > > > # free
    > > > total used free shared buffers cached
    > > > Mem: 1933 920 1012 0 0 356
    > > > -/+ buffers/cache: 563 1369
    > > > Swap: 0 0 0
    > > >
    > > > It seems that the preallocated memory is not freed on -ENOMEM.
    > >
    > > Ah, this was my fault.
    > >
    > > I used to do this debugging trick:
    > >
    > > @@ -1207,7 +1207,7 @@ int hibernate_preallocate_memory(void)
    > > pages, size);
    > > swsusp_show_speed(&start, &stop, pages, "Allocated");
    > >
    > > - return 0;
    > > + return -ENOMEM;
    > >
    > > err_out:
    > > printk(KERN_CONT "\n");
    > >
    > > That "return -ENOMEM" should be "error = -ENOMEM" :-)
    > >
    > > Here is one more run:
    > >
    > > [ 194.016991] PM: Preallocating image memory ... done (allocated 383897 pages, 128000 image pages kept)
    > > [ 196.505999] PM: Allocated 1535588 kbytes in 2.47 seconds (621.69 MB/s)
    > >
    > > Now the free report is back to normal:
    > >
    > > # free
    > > total used free shared buffers cached
    > > Mem: 1933 74 1858 0 0 15

    The above 'free' still exposed something wrong: only 74M memory are left,
    instead of image_size=500M memory. I'm prepared to test your updated patches :-)


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