From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 0E59E6B0253 for ; Mon, 23 May 2016 13:44:42 -0400 (EDT) Received: by mail-wm0-f71.google.com with SMTP id a136so14849407wme.1 for ; Mon, 23 May 2016 10:44:42 -0700 (PDT) Received: from mail-lb0-x244.google.com (mail-lb0-x244.google.com. [2a00:1450:4010:c04::244]) by mx.google.com with ESMTPS id 66si19100546lfb.222.2016.05.23.10.44.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 23 May 2016 10:44:40 -0700 (PDT) Received: by mail-lb0-x244.google.com with SMTP id u2so3278450lbo.0 for ; Mon, 23 May 2016 10:44:40 -0700 (PDT) Date: Mon, 23 May 2016 20:44:37 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH 3/3] mm, thp: make swapin readahead under down_read of mmap_sem Message-ID: <20160523174437.GA3317@node.shutemov.name> References: <1464023651-19420-1-git-send-email-ebru.akagunduz@gmail.com> <1464023651-19420-4-git-send-email-ebru.akagunduz@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1464023651-19420-4-git-send-email-ebru.akagunduz@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Ebru Akagunduz Cc: linux-mm@kvack.org, hughd@google.com, riel@redhat.com, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, iamjoonsoo.kim@lge.com, gorcunov@openvz.org, linux-kernel@vger.kernel.org, mgorman@suse.de, rientjes@google.com, vbabka@suse.cz, aneesh.kumar@linux.vnet.ibm.com, hannes@cmpxchg.org, mhocko@suse.cz, boaz@plexistor.com On Mon, May 23, 2016 at 08:14:11PM +0300, Ebru Akagunduz wrote: > Currently khugepaged makes swapin readahead under > down_write. This patch supplies to make swapin > readahead under down_read instead of down_write. > > The patch was tested with a test program that allocates > 800MB of memory, writes to it, and then sleeps. The system > was forced to swap out all. Afterwards, the test program > touches the area by writing, it skips a page in each > 20 pages of the area. > > Signed-off-by: Ebru Akagunduz > --- > mm/huge_memory.c | 33 +++++++++++++++++++++++++++------ > 1 file changed, 27 insertions(+), 6 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index feee44c..668bc07 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2386,13 +2386,14 @@ static bool hugepage_vma_check(struct vm_area_struct *vma) > * but with mmap_sem held to protect against vma changes. > */ > > -static void __collapse_huge_page_swapin(struct mm_struct *mm, > +static bool __collapse_huge_page_swapin(struct mm_struct *mm, > struct vm_area_struct *vma, > unsigned long address, pmd_t *pmd) > { > unsigned long _address; > pte_t *pte, pteval; > int swapped_in = 0, ret = 0; > + struct vm_area_struct *vma_orig = vma; > > pte = pte_offset_map(pmd, address); > for (_address = address; _address < address + HPAGE_PMD_NR*PAGE_SIZE; > @@ -2402,11 +2403,19 @@ static void __collapse_huge_page_swapin(struct mm_struct *mm, > continue; > swapped_in++; > ret = do_swap_page(mm, vma, _address, pte, pmd, > - FAULT_FLAG_ALLOW_RETRY|FAULT_FLAG_RETRY_NOWAIT, > + FAULT_FLAG_ALLOW_RETRY, > pteval); > + /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */ > + if (ret & VM_FAULT_RETRY) { > + down_read(&mm->mmap_sem); > + vma = find_vma(mm, address); > + /* vma is no longer available, don't continue to swapin */ > + if (vma != vma_orig) > + return false; > + } > if (ret & VM_FAULT_ERROR) { > trace_mm_collapse_huge_page_swapin(mm, swapped_in, 0); > - return; > + return false; > } > /* pte is unmapped now, we need to map it */ > pte = pte_offset_map(pmd, _address); > @@ -2414,6 +2423,7 @@ static void __collapse_huge_page_swapin(struct mm_struct *mm, > pte--; > pte_unmap(pte); > trace_mm_collapse_huge_page_swapin(mm, swapped_in, 1); > + return true; > } > > static void collapse_huge_page(struct mm_struct *mm, > @@ -2459,7 +2469,7 @@ static void collapse_huge_page(struct mm_struct *mm, > * gup_fast later hanlded by the ptep_clear_flush and the VM > * handled by the anon_vma lock + PG_lock. > */ > - down_write(&mm->mmap_sem); > + down_read(&mm->mmap_sem); > if (unlikely(khugepaged_test_exit(mm))) { > result = SCAN_ANY_PROCESS; > goto out; > @@ -2490,9 +2500,20 @@ static void collapse_huge_page(struct mm_struct *mm, > * Don't perform swapin readahead when the system is under pressure, > * to avoid unnecessary resource consumption. > */ > - if (allocstall == curr_allocstall && swap != 0) > - __collapse_huge_page_swapin(mm, vma, address, pmd); > + if (allocstall == curr_allocstall && swap != 0) { > + /* > + * __collapse_huge_page_swapin always returns with mmap_sem > + * locked. If it fails, release mmap_sem and jump directly > + * label out. Continuing to collapse causes inconsistency. > + */ > + if (!__collapse_huge_page_swapin(mm, vma, address, pmd)) { > + up_read(&mm->mmap_sem); > + goto out; > + } > + } > > + up_read(&mm->mmap_sem); > + down_write(&mm->mmap_sem); That's the critical point. How do you guarantee that the vma will not be destroyed (or changed) between up_read() and down_write()? You need at least find_vma() again. > anon_vma_lock_write(vma->anon_vma); > > pte = pte_offset_map(pmd, address); > -- > 1.9.1 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org