Messages in this thread Patch in this message |  | | From | Vineet Gupta <> | Subject | [PATCH 9/9] ARC: mm: do_page_fault refactor #8: release mmap_sem sooner | Date | Tue, 14 May 2019 17:29:36 -0700 |
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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 supe rhigh, 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 cabn stil 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 <peterz@infradead.org> Signed-off-by: Vineet Gupta <vgupta@synopsys.com> --- arch/arc/mm/fault.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c index 20402217d9da..e93ea06c214c 100644 --- a/arch/arc/mm/fault.c +++ b/arch/arc/mm/fault.c @@ -68,7 +68,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs) struct mm_struct *mm = tsk->mm; int sig, si_code = SEGV_MAPERR; unsigned int write = 0, exec = 0, mask; - vm_fault_t fault; /* handle_mm_fault() output */ + vm_fault_t fault = VM_FAULT_ERROR; /* handle_mm_fault() output */ unsigned int flags; /* handle_mm_fault() input */ /* @@ -155,6 +155,9 @@ void do_page_fault(unsigned long address, struct pt_regs *regs) } } +bad_area: + up_read(&mm->mmap_sem); + /* * Major/minor page fault accounting * (in case of retry we only land here once) @@ -173,13 +176,9 @@ void do_page_fault(unsigned long address, struct pt_regs *regs) } /* 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; -- 2.7.4
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