Messages in this thread | | | Subject | Re: [PATCH] mm: vmalloc: Remove double execution of vunmap_page_range | From | Chintan Pandya <> | Date | Fri, 13 Apr 2018 16:57:06 +0530 |
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On 4/13/2018 4:39 PM, Michal Hocko wrote: > On Fri 13-04-18 16:15:26, Chintan Pandya wrote: >> >> >> On 4/13/2018 4:10 PM, Anshuman Khandual wrote: >>> On 04/13/2018 03:47 PM, Chintan Pandya wrote: >>>> >>>> >>>> On 4/13/2018 3:29 PM, Anshuman Khandual wrote: >>>>> On 04/13/2018 02:46 PM, Chintan Pandya wrote: >>>>>> Unmap legs do call vunmap_page_range() irrespective of >>>>>> debug_pagealloc_enabled() is enabled or not. So, remove >>>>>> redundant check and optional vunmap_page_range() routines. >>>>> >>>>> vunmap_page_range() tears down the page table entries and does >>>>> not really flush related TLB entries normally unless page alloc >>>>> debug is enabled where it wants to make sure no stale mapping is >>>>> still around for debug purpose. Deferring TLB flush improves >>>>> performance. This patch will force TLB flush during each page >>>>> table tear down and hence not desirable. >>>>> >>>> Deferred TLB invalidation will surely improve performance. But force >>>> flush can help in detecting invalid access right then and there. I >>> >>> Deferred TLB invalidation was a choice made some time ago with the >>> commit db64fe02258f1507e ("mm: rewrite vmap layer") as these vmalloc >>> mappings wont be used other than inside the kernel and TLB gets >>> flushed when they are reused. This way it can still avail the benefit >>> of deferred TLB flushing without exposing itself to invalid accesses. >>> >>>> chose later. May be I should have clean up the vmap tear down code >>>> as well where it actually does the TLB invalidation. >>>> >>>> Or make TLB invalidation in free_unmap_vmap_area() be dependent upon >>>> debug_pagealloc_enabled(). >>> >>> Immediate TLB invalidation needs to be dependent on debug_pagealloc_ >>> enabled() and should be done only for debug purpose. Contrary to that >>> is not desirable. >>> >> Okay. I will raise v2 for that. > > More importantly. Your changelog absolutely lacks the _why_ part. It > just states what the code does which is not all that hard to read from > the diff. It is usually much more important to present _why_ the patch > is an improvement and worth merging. >
It is improving performance in debug scenario. More than that, I see it as a clean up. Sure, I will try to address *why* in next change log.
Chintan -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
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