Messages in this thread | | | Subject | Re: [PATCH] mm: vmalloc: Remove double execution of vunmap_page_range | From | Chintan Pandya <> | Date | Fri, 13 Apr 2018 16:15:26 +0530 |
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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.
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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