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Date: Tue, 5 May 2009 10:24:27 +0800 From: Wu Fengguang <fengguang.wu@...el.com> To: "Rafael J. Wysocki" <rjw@...k.pl> Cc: "linux-pm@...ts.linux-foundation.org" <linux-pm@...ts.linux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, "pavel@....cz" <pavel@....cz>, "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>, "jens.axboe@...cle.com" <jens.axboe@...cle.com>, "alan-jenkins@...fmail.co.uk" <alan-jenkins@...fmail.co.uk>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kernel-testers@...r.kernel.org" <kernel-testers@...r.kernel.org> Subject: Re: [PATCH 5/5] PM/Hibernate: Do not release preallocated memory unnecessarily (rev. 2) On Mon, May 04, 2009 at 08:22:38AM +0800, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rjw@...k.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. + error = memory_bm_create(&orig_bm, GFP_IMAGE, PG_ANY); + if (error) + goto err_out; + + error = memory_bm_create(©_bm, GFP_IMAGE, PG_ANY); + if (error) + goto err_out; memory_bm_create() is called a number of times, each time it will call create_mem_extents()/memory_bm_free(). Can they be optimized to be called only once? A side note: there are somehow duplicated *_extent_*() logics in the filesystems, is it possible that we abstract out some of the common code? + 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]; + } Why [ZONE_NORMAL] instead of [zone]? ZONE_NORMAL may not always be the largest zone, for example, My 4GB laptop has a tiny ZONE_NORMAL and a large ZONE_DMA32. + /* If size < max_size, preallocating enough memory may be impossible. */ + if (count > 0 && size == max_size) + error = -ENOMEM; + if (error) + goto err_out; The two if()s can be merged. At last, I'd express my major concern about the transition to preallocate based memory shrinking: will it lead to more random swapping IOs? Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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