From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757151AbbFPVPn (ORCPT ); Tue, 16 Jun 2015 17:15:43 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36605 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754792AbbFPVPl (ORCPT ); Tue, 16 Jun 2015 17:15:41 -0400 Date: Tue, 16 Jun 2015 14:15:40 -0700 From: Andrew Morton To: Ebru Akagunduz Cc: linux-mm@kvack.org, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, riel@redhat.com, iamjoonsoo.kim@lge.com, xiexiuqi@huawei.com, gorcunov@openvz.org, linux-kernel@vger.kernel.org, mgorman@suse.de, rientjes@google.com, vbabka@suse.cz, aneesh.kumar@linux.vnet.ibm.com, hughd@google.com, hannes@cmpxchg.org, mhocko@suse.cz, boaz@plexistor.com, raindel@mellanox.com Subject: Re: [RFC 3/3] mm: make swapin readahead to improve thp collapse rate Message-Id: <20150616141540.adc40130139151bf19f07ff9@linux-foundation.org> In-Reply-To: <1434294283-8699-4-git-send-email-ebru.akagunduz@gmail.com> References: <1434294283-8699-1-git-send-email-ebru.akagunduz@gmail.com> <1434294283-8699-4-git-send-email-ebru.akagunduz@gmail.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 14 Jun 2015 18:04:43 +0300 Ebru Akagunduz wrote: > This patch makes swapin readahead to improve thp collapse rate. > When khugepaged scanned pages, there can be a few of the pages > in swap area. > > With the patch THP can collapse 4kB pages into a THP when > there are up to max_ptes_swap swap ptes in a 2MB range. > > The patch was tested with a test program that allocates > 800MB of memory, writes to it, and then sleeps. I force > the system to swap out all. Afterwards, the test program > touches the area by writing, it skips a page in each > 20 pages of the area. > > Without the patch, system did not swap in readahead. > THP rate was %47 of the program of the memory, it > did not change over time. > > With this patch, after 10 minutes of waiting khugepaged had > collapsed %99 of the program's memory. > > ... > > +/* > + * Bring missing pages in from swap, to complete THP collapse. > + * Only done if khugepaged_scan_pmd believes it is worthwhile. > + * > + * Called and returns without pte mapped or spinlocks held, > + * but with mmap_sem held to protect against vma changes. > + */ > + > +static void __collapse_huge_page_swapin(struct mm_struct *mm, > + struct vm_area_struct *vma, > + unsigned long address, pmd_t *pmd, > + pte_t *pte) > +{ > + unsigned long _address; > + pte_t pteval = *pte; > + int swap_pte = 0; > + > + pte = pte_offset_map(pmd, address); > + for (_address = address; _address < address + HPAGE_PMD_NR*PAGE_SIZE; > + pte++, _address += PAGE_SIZE) { > + pteval = *pte; > + if (is_swap_pte(pteval)) { > + swap_pte++; > + do_swap_page(mm, vma, _address, pte, pmd, 0x0, pteval); > + /* pte is unmapped now, we need to map it */ > + pte = pte_offset_map(pmd, _address); > + } > + } > + pte--; > + pte_unmap(pte); > + trace_mm_collapse_huge_page_swapin(mm, vma->vm_start, swap_pte); > +} This is doing a series of synchronous reads. That will be sloooow on spinning disks. This function should be significantly faster if it first gets all the necessary I/O underway. I don't think we have a function which exactly does this. Perhaps generalise swapin_readahead() or open-code something like blk_start_plug(...); for (_address = address; _address < address + HPAGE_PMD_NR*PAGE_SIZE; pte++, _address += PAGE_SIZE) { if (is_swap_pte(*pte)) { read_swap_cache_async(...); } } blk_finish_plug(...); If you do make a change such as this, please benchmark its effects. Not on SSD ;) From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f181.google.com (mail-pd0-f181.google.com [209.85.192.181]) by kanga.kvack.org (Postfix) with ESMTP id D2E3D6B0038 for ; Tue, 16 Jun 2015 17:15:42 -0400 (EDT) Received: by pdjn11 with SMTP id n11so22571955pdj.0 for ; Tue, 16 Jun 2015 14:15:42 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id tv5si2887991pbc.226.2015.06.16.14.15.41 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 Jun 2015 14:15:41 -0700 (PDT) Date: Tue, 16 Jun 2015 14:15:40 -0700 From: Andrew Morton Subject: Re: [RFC 3/3] mm: make swapin readahead to improve thp collapse rate Message-Id: <20150616141540.adc40130139151bf19f07ff9@linux-foundation.org> In-Reply-To: <1434294283-8699-4-git-send-email-ebru.akagunduz@gmail.com> References: <1434294283-8699-1-git-send-email-ebru.akagunduz@gmail.com> <1434294283-8699-4-git-send-email-ebru.akagunduz@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Ebru Akagunduz Cc: linux-mm@kvack.org, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, riel@redhat.com, iamjoonsoo.kim@lge.com, xiexiuqi@huawei.com, gorcunov@openvz.org, linux-kernel@vger.kernel.org, mgorman@suse.de, rientjes@google.com, vbabka@suse.cz, aneesh.kumar@linux.vnet.ibm.com, hughd@google.com, hannes@cmpxchg.org, mhocko@suse.cz, boaz@plexistor.com, raindel@mellanox.com On Sun, 14 Jun 2015 18:04:43 +0300 Ebru Akagunduz wrote: > This patch makes swapin readahead to improve thp collapse rate. > When khugepaged scanned pages, there can be a few of the pages > in swap area. > > With the patch THP can collapse 4kB pages into a THP when > there are up to max_ptes_swap swap ptes in a 2MB range. > > The patch was tested with a test program that allocates > 800MB of memory, writes to it, and then sleeps. I force > the system to swap out all. Afterwards, the test program > touches the area by writing, it skips a page in each > 20 pages of the area. > > Without the patch, system did not swap in readahead. > THP rate was %47 of the program of the memory, it > did not change over time. > > With this patch, after 10 minutes of waiting khugepaged had > collapsed %99 of the program's memory. > > ... > > +/* > + * Bring missing pages in from swap, to complete THP collapse. > + * Only done if khugepaged_scan_pmd believes it is worthwhile. > + * > + * Called and returns without pte mapped or spinlocks held, > + * but with mmap_sem held to protect against vma changes. > + */ > + > +static void __collapse_huge_page_swapin(struct mm_struct *mm, > + struct vm_area_struct *vma, > + unsigned long address, pmd_t *pmd, > + pte_t *pte) > +{ > + unsigned long _address; > + pte_t pteval = *pte; > + int swap_pte = 0; > + > + pte = pte_offset_map(pmd, address); > + for (_address = address; _address < address + HPAGE_PMD_NR*PAGE_SIZE; > + pte++, _address += PAGE_SIZE) { > + pteval = *pte; > + if (is_swap_pte(pteval)) { > + swap_pte++; > + do_swap_page(mm, vma, _address, pte, pmd, 0x0, pteval); > + /* pte is unmapped now, we need to map it */ > + pte = pte_offset_map(pmd, _address); > + } > + } > + pte--; > + pte_unmap(pte); > + trace_mm_collapse_huge_page_swapin(mm, vma->vm_start, swap_pte); > +} This is doing a series of synchronous reads. That will be sloooow on spinning disks. This function should be significantly faster if it first gets all the necessary I/O underway. I don't think we have a function which exactly does this. Perhaps generalise swapin_readahead() or open-code something like blk_start_plug(...); for (_address = address; _address < address + HPAGE_PMD_NR*PAGE_SIZE; pte++, _address += PAGE_SIZE) { if (is_swap_pte(*pte)) { read_swap_cache_async(...); } } blk_finish_plug(...); If you do make a change such as this, please benchmark its effects. Not on SSD ;) -- 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