Re: [RFC][PATCH -mm] swsusp: use less memory during resume

[Pavel Machek <pavel@ucw.cz>]

Hi!

> Currently during resume swsusp puts the image data in the page frames that
> don't conflict with the original locations of the data (ie. the locations the
> data will be put in when the saved system state is restored from the image).
> These page frames are considered as "safe" and the other page frames are
> treadet as "unsafe".
> 
> Of course we cannot force the memory allocator to allocate "safe" pages only,
> so if an "unsafe" page is allocated, swsusp treats it as an "eaten page" and
> attempts to allocate another page in the hope that it'll be "safe" etc.
> swsusp tries to allocate as many "safe" pages as necessary to store the
> image data, so it "eats" a considerable number of "unsafe" pages in the
> process.  Next, it reads the image and puts the data into the allocated "safe"
> pages.  Finally, the data are copied to their "original" locations.
> 
> This approach, although it works nicely, is quite inefficient from the memory
> utilization point of view and it also turns out to be unnecessary.  Namely,
> for each "unsafe" page frame returned by the memory allocator there's exactly
> one page in the image that finally should be placed in this page frame.
> Therefore we can put the right data into this page frame as soon as they're
> read from the image and we won't have to copy these data later on.  This way
> we'll only need to allocate as many pages as necessary to store the image
> data and we won't have to "eat" the "unsafe" pages.

Looks good to me. Clever hack, I'd say.
									Pavel
-- 
Thanks for all the (sleeping) penguins.
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