Messages in this thread | | | Date | Fri, 7 May 2010 12:24:50 +0300 | Subject | Re: [PATCH 1/3] Add flag to identify block swap devices | From | Pekka Enberg <> |
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On Fri, May 7, 2010 at 5:16 PM, Nitin Gupta <ngupta@vflare.org> wrote: >> On 05/07/2010 01:33 PM, jassi brar wrote: >>> On Fri, May 7, 2010 at 4:25 PM, Nitin Gupta <ngupta@vflare.org> wrote: >>>> Added SWP_BLKDEV flag to distinguish block and regular file backed >>>> swap devices. We could also check if a swap is entire block device, >>>> rather than a file, by: >>>> S_ISBLK(swap_info_struct->swap_file->f_mapping->host->i_mode) >>>> but, I think, simply checking this flag is more convenient. >>> This might make it convenient for now but is likely to increase complexity and >>> redundancy. Why not define a macro/inline to figure that out? >>> >> >> Accessing such long pointer chain is maybe not good thing to do for >> every swap_entry_free() call? Simple checking a flag is perhaps slightly >> faster? I also can't see how this flag can later increase complexity >> compared to creating new macro for this check. > > I am not sure about effects on the speed, that needs to be seen. > But here are points against using a new flag....
On Fri, May 7, 2010 at 11:56 AM, jassi brar <jassisinghbrar@gmail.com> wrote: > a) Defining a new flag hogs up precious real-estate of remaining just 2 bits > (apparently the new flags are to go before SWP_SCANNING) > > b) Over time, some dependent code might evolve to depend upon this flag, while > others might use the indirection to deduct if it is block device > or not. That > will make it complicated to make any relevant change in future as we'll have > to keep track of more than one way to check the status. Creating a new > macro doesn't create a new path to reach the status, but a FLAG does.
I think the flag is cleaner and I'm not convinced by the above speculative arguments that we should switch to a static inline function.
Hugh, Linus, would you mind voicing your opinion which way to go here? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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