On 06/15/2012 09:35 AM, Dan Magenheimer wrote: >> From: Seth Jennings [mailto:sjenning@xxxxxxxxxxxxxxxxxx] >> Sent: Friday, June 15, 2012 9:13 AM >> To: Peter Zijlstra >> Cc: Minchan Kim; Greg Kroah-Hartman; Nitin Gupta; Dan Magenheimer; linux-kernel@xxxxxxxxxxxxxxx; >> linux-mm@xxxxxxxxx; Thomas Gleixner; Ingo Molnar; Tejun Heo; David Howells; x86@xxxxxxxxxx; Nick >> Piggin >> Subject: Re: [PATCH v2 3/3] x86: Support local_flush_tlb_kernel_range >> >> On 05/17/2012 09:51 AM, Peter Zijlstra wrote: >> >>> On Thu, 2012-05-17 at 17:11 +0900, Minchan Kim wrote: >>>>> +++ b/arch/x86/include/asm/tlbflush.h >>>>> @@ -172,4 +172,16 @@ static inline void flush_tlb_kernel_range(unsigned long start, >>>>> flush_tlb_all(); >>>>> } >>>>> >>>>> +static inline void local_flush_tlb_kernel_range(unsigned long start, >>>>> + unsigned long end) >>>>> +{ >>>>> + if (cpu_has_invlpg) { >>>>> + while (start < end) { >>>>> + __flush_tlb_single(start); >>>>> + start += PAGE_SIZE; >>>>> + } >>>>> + } else >>>>> + local_flush_tlb(); >>>>> +} >>> >>> It would be much better if you wait for Alex Shi's patch to mature. >>> doing the invlpg thing for ranges is not an unconditional win. >> >> From what I can tell Alex's patches have stalled. The last post was v6 >> on 5/17 and there wasn't a single reply to them afaict. >> >> According to Alex's investigation of this "tipping point", it seems that >> a good generic value is 8. In other words, on most x86 hardware, it is >> cheaper to flush up to 8 tlb entries one by one rather than doing a >> complete flush. >> >> So we can do something like: >> >> if (cpu_has_invlpg && (end - start)/PAGE_SIZE <= 8) { >> while (start < end) { >> >> Would this be acceptable? > > Hey Seth, Nitin -- > > After more work digging around zsmalloc and zbud, I really think > this TLB flushing, as well as the "page pair mapping" code can be > completely eliminated IFF zsmalloc is limited to items PAGE_SIZE or > less. Since this is already true of zram (and in-tree zcache), and > zsmalloc currently has no other users, I think you should seriously > consider limiting zsmalloc in that way, or possibly splitting out > one version of zsmalloc which handles items PAGE_SIZE or less, > and a second version that can handle larger items but has (AFAIK) > no users. > > If you consider it an option to have (a version of) zsmalloc > limited to items PAGE_SIZE or less, let me know and we can > get into the details. > zsmalloc is already limited to objects of size PAGE_SIZE or less. This two-page splitting is for efficiently storing objects in range (PAGE_SIZE/2, PAGE_SIZE) which is very common in both zram and zcache. SLUB achieves this efficiency by allocating higher order pages but that is not an option for zsmalloc. 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>