From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757570AbbFQDUi (ORCPT ); Tue, 16 Jun 2015 23:20:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51134 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752723AbbFQDUa (ORCPT ); Tue, 16 Jun 2015 23:20:30 -0400 Message-ID: <5580E774.3070307@redhat.com> Date: Tue, 16 Jun 2015 23:20:20 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Andrew Morton , Ebru Akagunduz CC: linux-mm@kvack.org, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@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 References: <1434294283-8699-1-git-send-email-ebru.akagunduz@gmail.com> <1434294283-8699-4-git-send-email-ebru.akagunduz@gmail.com> <20150616141540.adc40130139151bf19f07ff9@linux-foundation.org> In-Reply-To: <20150616141540.adc40130139151bf19f07ff9@linux-foundation.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/16/2015 05:15 PM, Andrew Morton wrote: > 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 Looking at do_swap_page() and __lock_page_or_retry(), I guess there already is a way to do the above. Passing a "flags" of FAULT_FLAG_ALLOW_RETRY|FAULT_FLAG_RETRY_NOWAIT to do_swap_page() should result in do_swap_page() returning with the pte unmapped and the mmap_sem still held if the page was not immediately available to map into the pte (trylock_page succeeds). Ebru, can you try passing the above as the flags argument to do_swap_page(), and see what happens? -- All rights reversed From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qg0-f52.google.com (mail-qg0-f52.google.com [209.85.192.52]) by kanga.kvack.org (Postfix) with ESMTP id 511DD6B0032 for ; Tue, 16 Jun 2015 23:20:32 -0400 (EDT) Received: by qgeu36 with SMTP id u36so11583017qge.2 for ; Tue, 16 Jun 2015 20:20:32 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id r14si3086658qha.35.2015.06.16.20.20.31 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 Jun 2015 20:20:31 -0700 (PDT) Message-ID: <5580E774.3070307@redhat.com> Date: Tue, 16 Jun 2015 23:20:20 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [RFC 3/3] mm: make swapin readahead to improve thp collapse rate References: <1434294283-8699-1-git-send-email-ebru.akagunduz@gmail.com> <1434294283-8699-4-git-send-email-ebru.akagunduz@gmail.com> <20150616141540.adc40130139151bf19f07ff9@linux-foundation.org> In-Reply-To: <20150616141540.adc40130139151bf19f07ff9@linux-foundation.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , Ebru Akagunduz Cc: linux-mm@kvack.org, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@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 06/16/2015 05:15 PM, Andrew Morton wrote: > 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 Looking at do_swap_page() and __lock_page_or_retry(), I guess there already is a way to do the above. Passing a "flags" of FAULT_FLAG_ALLOW_RETRY|FAULT_FLAG_RETRY_NOWAIT to do_swap_page() should result in do_swap_page() returning with the pte unmapped and the mmap_sem still held if the page was not immediately available to map into the pte (trylock_page succeeds). Ebru, can you try passing the above as the flags argument to do_swap_page(), and see what happens? -- All rights reversed -- 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