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Commit 1d828b7c authored by Mahendran Ganesh's avatar Mahendran Ganesh Committed by Vinayak Menon
Browse files

arm64/mm: add speculative page fault 



This patch enables the speculative page fault on the arm64
architecture.

I completed spf porting in 4.9. From the test result,
we can see app launching time improved by about 10% in average.
For the apps which have more than 50 threads, 15% or even more
improvement can be got.

Change-Id: Ib7c8b2e354800b5023e6c6400448a6d40aaf89c8
Signed-off-by: default avatarGanesh Mahendran <opensource.ganesh@gmail.com>
Patch-mainline: linux-mm @ Wed, 2 May 2018 15:54:32
[vinmenon@codeaurora.org: remove the speculative fault perf counter
plus 4.9 porting conflict fixes - rearrange the __do_page_fault code
to make it work fine with speculative page fault]
Signed-off-by: default avatarVinayak Menon <vinmenon@codeaurora.org>
parent c3e566a6

arch/arm64/mm/fault.c

+45 −24
Original line number Diff line number Diff line
@@ -253,14 +253,12 @@ static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *re 
#define VM_FAULT_BADMAP		0x010000

#define VM_FAULT_BADACCESS	0x020000



static int __do_page_fault(struct mm_struct *mm, unsigned long addr,

static int __do_page_fault(struct vm_area_struct *vma, unsigned long addr,

			   unsigned int mm_flags, unsigned long vm_flags,

			   struct task_struct *tsk)

{

	struct vm_area_struct *vma;

	int fault;



	vma = find_vma(mm, addr);

	fault = VM_FAULT_BADMAP;

	if (unlikely(!vma))

		goto out;
@@ -318,6 +316,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, 
	int fault, sig, code;

	unsigned long vm_flags = VM_READ | VM_WRITE;

	unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

	struct vm_area_struct *vma = NULL;



	if (notify_page_fault(regs, esr))

		return 0;
@@ -355,6 +354,14 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, 
			die("Accessing user space memory outside uaccess.h routines", regs, esr);

	}



	/*

	 * let's try a speculative page fault without grabbing the

	 * mmap_sem.

	 */

	fault = handle_speculative_fault(mm, addr, mm_flags, &vma);

	if (fault != VM_FAULT_RETRY)

		goto done;



	/*

	 * As per x86, we may deadlock here. However, since the kernel only

	 * validly references user space from well defined areas of the code,
@@ -377,19 +384,44 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, 
#endif

	}



	fault = __do_page_fault(mm, addr, mm_flags, vm_flags, tsk);

	if (!vma || !can_reuse_spf_vma(vma, addr))

		vma = find_vma(mm, addr);



	fault = __do_page_fault(vma, addr, mm_flags, vm_flags, tsk);

	if (fault & VM_FAULT_RETRY) {

		/*

		 * If we need to retry but a fatal signal is pending, handle the

	 * signal first. We do not need to release the mmap_sem because it

	 * would already be released in __lock_page_or_retry in mm/filemap.c.

		 * signal first. We do not need to release the mmap_sem because

		 * it would already be released in __lock_page_or_retry in

		 * mm/filemap.c.

		 */

	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {



		if (fatal_signal_pending(current)) {

			if (!user_mode(regs))

				goto no_context;

			return 0;

		}



		/*

		 * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk of

		 * starvation.

		 */

		if (mm_flags & FAULT_FLAG_ALLOW_RETRY) {

			mm_flags &= ~FAULT_FLAG_ALLOW_RETRY;

			mm_flags |= FAULT_FLAG_TRIED;



			/*

			 * Do not try to reuse this vma and fetch it

			 * again since we will release the mmap_sem.

			 */

			vma = NULL;

			goto retry;

		}

	}



	up_read(&mm->mmap_sem);

done:



	/*

	 * Major/minor page fault accounting is only done on the initial

	 * attempt. If we go through a retry, it is extremely likely that the
@@ -407,19 +439,8 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, 
			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs,

				      addr);

		}

		if (fault & VM_FAULT_RETRY) {

			/*

			 * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk of

			 * starvation.

			 */

			mm_flags &= ~FAULT_FLAG_ALLOW_RETRY;

			mm_flags |= FAULT_FLAG_TRIED;

			goto retry;

		}

	}



	up_read(&mm->mmap_sem);



	/*

	 * Handle the "normal" case first - VM_FAULT_MAJOR

	 */