linux-kernel - Re: [PATCH] mm/swap_slots: use conditional compilation for swap

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Date:   Tue, 30 Jan 2018 15:54:45 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Randy Dunlap <rdunlap@...radead.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/swap_slots: use conditional compilation for
 swap_slots.c

On 01/30/2018 03:14 PM, Randy Dunlap wrote:
> From: Randy Dunlap <rdunlap@...radead.org>
> 
> For mm/swap_slots.c, use the traditional Linux method of conditional
> compilation and linking instead of always compiling it by using
> #ifdef CONFIG_SWAP and #endif for the entire source file (excluding
> header files).
> 
> Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
> ---
>  mm/Makefile     |    4 ++--
>  mm/swap_slots.c |    4 ----
>  2 files changed, 2 insertions(+), 6 deletions(-)
> 
> Tim, is there some reason that this is done as it currently is?

Rearranging code the way you have proposed makes sense.
You can add my ack.

Thanks.

Tim

> 
> --- lnx-415.orig/mm/Makefile
> +++ lnx-415/mm/Makefile
> @@ -37,7 +37,7 @@ obj-y			:= filemap.o mempool.o oom_kill.
>  			   readahead.o swap.o truncate.o vmscan.o shmem.o \
>  			   util.o mmzone.o vmstat.o backing-dev.o \
>  			   mm_init.o mmu_context.o percpu.o slab_common.o \
> -			   compaction.o vmacache.o swap_slots.o \
> +			   compaction.o vmacache.o \
>  			   interval_tree.o list_lru.o workingset.o \
>  			   debug.o $(mmu-y)
>  
> @@ -55,7 +55,7 @@ ifdef CONFIG_MMU
>  endif
>  obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
>  
> -obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o
> +obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o swap_slots.o
>  obj-$(CONFIG_FRONTSWAP)	+= frontswap.o
>  obj-$(CONFIG_ZSWAP)	+= zswap.o
>  obj-$(CONFIG_HAS_DMA)	+= dmapool.o
> --- lnx-415.orig/mm/swap_slots.c
> +++ lnx-415/mm/swap_slots.c
> @@ -34,8 +34,6 @@
>  #include <linux/mutex.h>
>  #include <linux/mm.h>
>  
> -#ifdef CONFIG_SWAP
> -
>  static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots);
>  static bool	swap_slot_cache_active;
>  bool	swap_slot_cache_enabled;
> @@ -356,5 +354,3 @@ repeat:
>  
>  	return entry;
>  }
> -
> -#endif /* CONFIG_SWAP */
> 
>