On 06/07/2012 01:47 PM, Dan Magenheimer wrote: >> From: Minchan Kim [mailto:minchan@xxxxxxxxxx] >> Subject: Re: [PATCH 2/2] zram: clean up handle >> >> On 06/06/2012 02:04 PM, Nitin Gupta wrote: >> >>> On 06/05/2012 12:23 AM, Minchan Kim wrote: >>> >>>> zram's handle variable can store handle of zsmalloc in case of >>>> compressing efficiently. Otherwise, it stores point of page descriptor. >>>> This patch clean up the mess by union struct. >>>> >>>> changelog >>>> * from v1 >>>> - none(new add in v2) >>>> >>>> Cc: Nitin Gupta <ngupta@xxxxxxxxxx> >>>> Acked-by: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx> >>>> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> >>>> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> >>>> --- >>>> drivers/staging/zram/zram_drv.c | 77 ++++++++++++++++++++------------------- >>>> drivers/staging/zram/zram_drv.h | 5 ++- >>>> 2 files changed, 44 insertions(+), 38 deletions(-) >>> >>> I think page vs handle distinction was added since xvmalloc could not >>> handle full page allocation. Now that zsmalloc allows full page >> >> I see. I didn't know that because I'm blind on xvmalloc. >> >>> allocation, we can just use it for both cases. This would also allow >>> removing the ZRAM_UNCOMPRESSED flag. The only downside will be slightly >>> slower code path for full page allocation but this event is anyways >>> supposed to be rare, so should be fine. >> >> Fair enough. >> It can remove many code of zram. >> Okay. Will look into that. > > Nitin, can zsmalloc allow full page allocation by assigning > an actual physical pageframe (which is what zram does now)? > Or will it allocate PAGE_SIZE bytes which zsmalloc will allocate > crossing a page boundary which, presumably, will have much worse > impact on page allocator availability when these pages are > "reclaimed" via your swap notify callback. > zsmalloc does not add any object headers, so when allocating PAGE_SIZE you get a separate page from as if you did alloc_page(). So, it does not span page boundaries. > Though this may be rare across all workloads, it may turn out > to be very common for certain workloads (e.g. if the workload > has many dirty anonymous pages that are already compressed > by userland). > > It may not be worth cleaning up the code if it causes > performance issues with this case. > > And anyway can zsmalloc handle and identify to the caller pages > that are both compressed and "native" (uncompressed)? It > certainly has to handle both if you remove ZRAM_UNCOMPRESSED > as compressing some pages actually results in more than > PAGE_SIZE bytes. So you need to record somewhere that > this "compressed page" is special and that must somehow > be communicated to the caller of your "get" routine. > > (Just trying to save Minchan from removing all that code but > then needing to add it back again.) > zsmalloc cannot identify compressed vs uncompressed pages. However, in zram, we can tell if the page is uncompressed using table[i]->size which is set to PAGE_SIZE for uncompressed pages. Pages that compress to more than PAGE_SIZE (i.e. expand on compression) are stored as-is/uncompressed and thus will have size field set to PAGE_SIZE. Thus, we do not require ZRAM_UNCOMPRESSED flag when using zsmalloc for both compressed and uncompressed pages. Thanks, Nitin Thanks, Nitin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>