From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f71.google.com (mail-oi0-f71.google.com [209.85.218.71]) by kanga.kvack.org (Postfix) with ESMTP id D8CCB4403E0 for ; Wed, 8 Nov 2017 08:02:29 -0500 (EST) Received: by mail-oi0-f71.google.com with SMTP id j126so2030032oib.9 for ; Wed, 08 Nov 2017 05:02:29 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id o3si1889328oih.293.2017.11.08.05.02.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 08 Nov 2017 05:02:27 -0800 (PST) From: Vitaly Kuznetsov Subject: [PATCH RFC] mm/memory_hotplug: make it possible to offline blocks with reserved pages Date: Wed, 8 Nov 2017 14:01:55 +0100 Message-Id: <20171108130155.25499-1-vkuznets@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Michal Hocko , Vlastimil Babka , Mel Gorman , YASUAKI ISHIMATSU , Hillf Danton , Johannes Weiner , "K. Y. Srinivasan" , Stephen Hemminger , Alex Ng Hyper-V balloon driver needs to hotplug memory in smaller chunks and to workaround Linux's 128Mb allignment requirement so it does a trick: partly populated 128Mb blocks are added and then a custom online_page_callback hook checks if the particular page is 'backed' during onlining, in case it is not backed it is left in Reserved state. When the host adds more pages to the block we bring them online from the driver (see hv_bring_pgs_online()/hv_page_online_one() in drivers/hv/hv_balloon.c). Eventually the whole block becomes fully populated and we hotplug the next 128Mb. This all works for quite some time already. What is not working is offlining of such partly populated blocks: check_pages_isolated_cb() callback will not pass with a sinle Reserved page and we end up with -EBUSY. However, there's no reason to fail offlining in this case: these pages are already offline, we may just skip them. Add the appropriate workaround to test_pages_isolated(). Signed-off-by: Vitaly Kuznetsov --- RFC part: - Other usages of Reserved pages making offlining blocks with them a no-go may exist. - I'm not exactly sure that adding another parameter to test_pages_isolated() is a good idea, we may go with a single flag for both Reserved and HwPoisoned pages: we have just two call sites and they have opposite needs (true, true in one case and false, false in the other). --- include/linux/page-isolation.h | 2 +- mm/memory_hotplug.c | 2 +- mm/page_alloc.c | 8 +++++++- mm/page_isolation.c | 11 ++++++++--- 4 files changed, 17 insertions(+), 6 deletions(-) diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h index 05a04e603686..daba12a59574 100644 --- a/include/linux/page-isolation.h +++ b/include/linux/page-isolation.h @@ -61,7 +61,7 @@ undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn, * Test all pages in [start_pfn, end_pfn) are isolated or not. */ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn, - bool skip_hwpoisoned_pages); + bool skip_hwpoisoned_pages, bool skip_reserved_pages); struct page *alloc_migrate_target(struct page *page, unsigned long private, int **resultp); diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index d4b5f29906b9..5b7d1482804f 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1467,7 +1467,7 @@ check_pages_isolated_cb(unsigned long start_pfn, unsigned long nr_pages, { int ret; long offlined = *(long *)data; - ret = test_pages_isolated(start_pfn, start_pfn + nr_pages, true); + ret = test_pages_isolated(start_pfn, start_pfn + nr_pages, true, true); offlined = nr_pages; if (!ret) *(long *)data += offlined; diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 77e4d3c5c57b..b475928c476c 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -7632,7 +7632,7 @@ int alloc_contig_range(unsigned long start, unsigned long end, } /* Make sure the range is really isolated. */ - if (test_pages_isolated(outer_start, end, false)) { + if (test_pages_isolated(outer_start, end, false, false)) { pr_info_ratelimited("%s: [%lx, %lx) PFNs busy\n", __func__, outer_start, end); ret = -EBUSY; @@ -7746,6 +7746,12 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn) continue; } + /* Some pages might never be online, skip them */ + if (unlikely(PageReserved(page))) { + pfn++; + continue; + } + BUG_ON(page_count(page)); BUG_ON(!PageBuddy(page)); order = page_order(page); diff --git a/mm/page_isolation.c b/mm/page_isolation.c index 44f213935bf6..fd9c18e00b92 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -233,7 +233,8 @@ int undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn, */ static unsigned long __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn, - bool skip_hwpoisoned_pages) + bool skip_hwpoisoned_pages, + bool skip_reserved_pages) { struct page *page; @@ -253,6 +254,9 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn, else if (skip_hwpoisoned_pages && PageHWPoison(page)) /* A HWPoisoned page cannot be also PageBuddy */ pfn++; + else if (skip_reserved_pages && PageReserved(page)) + /* Skipping Reserved pages */ + pfn++; else break; } @@ -262,7 +266,7 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn, /* Caller should ensure that requested range is in a single zone */ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn, - bool skip_hwpoisoned_pages) + bool skip_hwpoisoned_pages, bool skip_reserved_pages) { unsigned long pfn, flags; struct page *page; @@ -285,7 +289,8 @@ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn, zone = page_zone(page); spin_lock_irqsave(&zone->lock, flags); pfn = __test_page_isolated_in_pageblock(start_pfn, end_pfn, - skip_hwpoisoned_pages); + skip_hwpoisoned_pages, + skip_reserved_pages); spin_unlock_irqrestore(&zone->lock, flags); trace_test_pages_isolated(start_pfn, end_pfn, pfn); -- 2.13.6 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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