Subject: Re: + zsmalloc-do-not-remap-dst-page-while-prepare-next-src-page.patch added to -mm tree

From: Sergey Senozhatsky <[email-masked]>
Date: Wed, 25 Mar 2015 14:42:30 +0900

On (03/24/15 14:03), [email-masked] wrote:
> The patch titled
>      Subject: zsmalloc: do not remap dst page while prepare next src page
> has been added to the -mm tree.  Its filename is
>      zsmalloc-do-not-remap-dst-page-while-prepare-next-src-page.patch
> 
> This patch should soon appear at
>     http://ozlabs.org/~akpm/mmots/broken-out/zsmalloc-do-not-remap-dst-page-while-prepare-next-src-page.patch
> and later at
>     http://ozlabs.org/~akpm/mmotm/broken-out/zsmalloc-do-not-remap-dst-page-while-prepare-next-src-page.patch
> 

Hello Stephen,

Heesub Shin has reported that this patch causes BUG_ON on ARM
(with CONFIG_DEBUG_HIGHMEM enabled). Could you please revert
it in linux-next 20150325?

	-ss

> ------------------------------------------------------
> From: Sergey Senozhatsky <[email-masked]>
> Subject: zsmalloc: do not remap dst page while prepare next src page
> 
> The object may belong to different pages.  zs_object_copy() handles this
> case and maps a new source page (get_next_page() and kmap_atomic()) when
> object crosses boundaries of the current source page.  But it also
> performs unnecessary kunmap/kmap_atomic of the destination page (it
> remains unchanged), which can be avoided.
> 
> Signed-off-by: Sergey Senozhatsky <[email-masked]>
> Cc: Minchan Kim <[email-masked]>
> Cc: Nitin Gupta <[email-masked]>
> Signed-off-by: Andrew Morton <[email-masked]>
> ---
> 
>  mm/zsmalloc.c |    2 --
>  1 file changed, 2 deletions(-)
> 
> diff -puN mm/zsmalloc.c~zsmalloc-do-not-remap-dst-page-while-prepare-next-src-page mm/zsmalloc.c
> --- a/mm/zsmalloc.c~zsmalloc-do-not-remap-dst-page-while-prepare-next-src-page
> +++ a/mm/zsmalloc.c
> @@ -1538,12 +1538,10 @@ static void zs_object_copy(unsigned long
>  			break;
>  
>  		if (s_off + size >= PAGE_SIZE) {
> -			kunmap_atomic(d_addr);
>  			kunmap_atomic(s_addr);
>  			s_page = get_next_page(s_page);
>  			BUG_ON(!s_page);
>  			s_addr = kmap_atomic(s_page);
> -			d_addr = kmap_atomic(d_page);
>  			s_size = class->size - written;
>  			s_off = 0;
>  		} else {
> _
> 
> Patches currently in -mm which might be from [email-masked] are
> 
> zram-cosmetic-zram_attr_ro-code-formatting-tweak.patch
> zram-use-idr-instead-of-zram_devices-array.patch
> zram-factor-out-device-reset-from-reset_store.patch
> zram-reorganize-code-layout.patch
> zram-add-dynamic-device-add-remove-functionality.patch
> zram-add-dynamic-device-add-remove-functionality-fix.patch
> zram-remove-max_num_devices-limitation.patch
> zram-report-every-added-and-removed-device.patch
> zram-trivial-correct-flag-operations-comment.patch
> zram-return-zram-device_id-value-from-zram_add.patch
> zram-introduce-automatic-device_id-generation.patch
> zram-introduce-automatic-device_id-generation-fix.patch
> zram-do-not-let-user-enforce-new-device-dev_id.patch
> zsmalloc-decouple-handle-and-object.patch
> zsmalloc-factor-out-obj_.patch
> zsmalloc-support-compaction.patch
> zsmalloc-adjust-zs_almost_full.patch
> zram-support-compaction.patch
> zsmalloc-record-handle-in-page-private-for-huge-object.patch
> zsmalloc-add-fullness-into-stat.patch
> zsmalloc-zsmalloc-documentation.patch
> zram-remove-num_migrated-device-attr.patch
> zram-move-compact_store-to-sysfs-functions-area.patch
> zram-use-generic-start-end-io-accounting.patch
> zram-describe-device-attrs-in-documentation.patch
> zram-export-new-io_stat-sysfs-attrs.patch
> zram-export-new-mm_stat-sysfs-attrs.patch
> zram-deprecate-zram-attrs-sysfs-nodes.patch
> zsmalloc-remove-synchronize_rcu-from-zs_compact.patch
> zsmalloc-remove-extra-cond_resched-in-__zs_compact.patch
> zsmalloc-do-not-remap-dst-page-while-prepare-next-src-page.patch
> zsmalloc-micro-optimize-zs_object_copy.patch
> cpumask-dont-perform-while-loop-in-cpumask_next_and.patch
> lib-lz4-pull-out-constant-tables.patch
> 
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