From 926150db8558dca59617c8786c3f91c239290ee1 Mon Sep 17 00:00:00 2001 From: Vineet Gupta Date: Tue, 14 May 2019 16:28:30 -0700 Subject: [PATCH] ARC: mm: do_page_fault refactor #8: release mmap_sem sooner In case of successful page fault handling, this patch releases mmap_sem before updating the perf stat event for major/minor faults. So even though the contention reduction is NOT super high, it is still an improvement. There's an additional code size improvement as we only have 2 up_read() calls now. Note to myself: -------------- 1. Given the way it is done, we are forced to move @bad_area label earlier causing the various "goto bad_area" cases to hit perf stat code. - PERF_COUNT_SW_PAGE_FAULTS is NOW updated for access errors which is what arm/arm64 seem to be doing as well (with slightly different code) - PERF_COUNT_SW_PAGE_FAULTS_{MAJ,MIN} must NOT be updated for the error case which is guarded by now setting @fault initial value to VM_FAULT_ERROR which serves both cases when handle_mm_fault() returns error or is not called at all. 2. arm/arm64 use two homebrew fault flags VM_FAULT_BAD{MAP,MAPACCESS} which I was inclined to add too but seems not needed for ARC - given that we have everything is 1 function we can still use goto - we setup si_code at the right place (arm* do that in the end) - we init fault already to error value which guards entry into perf stats event update Cc: Peter Zijlstra Signed-off-by: Vineet Gupta --- arch/arc/mm/fault.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c index 6a78a2d776a9..e7df5ef3877a 100644 --- a/arch/arc/mm/fault.c +++ b/arch/arc/mm/fault.c @@ -152,6 +152,9 @@ retry: } } +bad_area: + up_read(&mm->mmap_sem); + /* * Major/minor page fault accounting * (in case of retry we only land here once) @@ -170,13 +173,9 @@ retry: } /* Normal return path: fault Handled Gracefully */ - up_read(&mm->mmap_sem); return; } -bad_area: - up_read(&mm->mmap_sem); - if (!user_mode(regs)) goto no_context; -- 2.30.2