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Wed, 17 Mar 2021 11:18:11 +0000 (UTC) Received: from [10.36.112.124] (ovpn-112-124.ams2.redhat.com [10.36.112.124]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9FC03629DA; Wed, 17 Mar 2021 11:18:08 +0000 (UTC) Subject: Re: [PATCH v3 3/3] mm: fs: Invalidate BH LRU during page migration To: Minchan Kim , Andrew Morton Cc: linux-mm , LKML , joaodias@google.com, surenb@google.com, cgoldswo@codeaurora.org, willy@infradead.org, mhocko@suse.com, vbabka@suse.cz, linux-fsdevel@vger.kernel.org References: <20210310161429.399432-1-minchan@kernel.org> <20210310161429.399432-3-minchan@kernel.org> <1bdc93e5-e5d4-f166-c467-5b94ac347857@redhat.com> <1527f16f-4376-a10d-4e72-041926cf38da@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <239b45ff-dad0-6cd0-4f6e-18159185cd6d@redhat.com> Date: Wed, 17 Mar 2021 12:18:07 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Stat-Signature: jbp3u3wqbunq5iwy8j3cfztx7jqw6su1 X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 143F8E0001B4 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf30; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=170.10.133.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615979897-145637 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 16.03.21 19:26, Minchan Kim wrote: > On Fri, Mar 12, 2021 at 09:17:23AM -0800, Minchan Kim wrote: >> On Fri, Mar 12, 2021 at 10:33:48AM +0100, David Hildenbrand wrote: >>> On 12.03.21 10:03, David Hildenbrand wrote: >>>> On 10.03.21 17:14, Minchan Kim wrote: >>>>> ffer_head LRU caches will be pinned and thus cannot be migrated. >>>>> This can prevent CMA allocations from succeeding, which are often used >>>>> on platforms with co-processors (such as a DSP) that can only use >>>>> physically contiguous memory. It can also prevent memory >>>>> hot-unplugging from succeeding, which involves migrating at least >>>>> MIN_MEMORY_BLOCK_SIZE bytes of memory, which ranges from 8 MiB to 1 >>>>> GiB based on the architecture in use. >>>> >>>> Actually, it's memory_block_size_bytes(), which can be even bigger >>>> (IIRC, 128MiB..2 GiB on x86-64) that fails to get offlined. But that >>>> will prevent bigger granularity (e.g., a whole DIMM) from getting unplugged. >>>> >>>>> >>>>> Correspondingly, invalidate the BH LRU caches before a migration >>>>> starts and stop any buffer_head from being cached in the LRU caches, >>>>> until migration has finished. >>>> >>>> Sounds sane to me. >>>> >>> >>> Diving a bit into the code, I am wondering: >>> >>> >>> a) Are these buffer head pages marked as movable? >>> >>> IOW, are they either PageLRU() or __PageMovable()? >>> >>> >>> b) How do these pages end up on ZONE_MOVABLE or MIGRATE_CMA? >>> >>> I assume these pages come via >>> alloc_page_buffers()->alloc_buffer_head()->kmem_cache_zalloc(GFP_NOFS | >>> __GFP_ACCOUNT) >>> >> >> It's indirect it was not clear >> >> try_to_release_page >> try_to_free_buffers >> buffer_busy >> failed >> >> Yeah, comment is misleading. This one would be better. >> >> /* >> * the refcount of buffer_head in bh_lru prevents dropping the >> * attached page(i.e., try_to_free_buffers) so it could cause >> * failing page migrationn. >> * Skip putting upcoming bh into bh_lru until migration is done. >> */ > Thanks, that makes more sense to me now :) > Hi Andrew, > > Could you fold this comment fix patch? If you prefer formal patch, > let me know. I will resend it. > > Thank you. > > From 0774f21e2dc8220fc2be80c25f711cb061363519 Mon Sep 17 00:00:00 2001 > From: Minchan Kim > Date: Fri, 12 Mar 2021 09:17:34 -0800 > Subject: [PATCH] comment fix > > Signed-off-by: Minchan Kim > --- > fs/buffer.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/fs/buffer.c b/fs/buffer.c > index ca9dd736bcb8..8602dcbe0327 100644 > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -1265,8 +1265,9 @@ static void bh_lru_install(struct buffer_head *bh) > > check_irqs_on(); > /* > - * buffer_head in bh_lru could increase refcount of the page > - * until it will be invalidated. It causes page migraion failure. > + * the refcount of buffer_head in bh_lru prevents dropping the > + * attached page(i.e., try_to_free_buffers) so it could cause > + * failing page migratoin. s/migratoin/migration/ > * Skip putting upcoming bh into bh_lru until migration is done. > */ > if (lru_cache_disabled()) > Acked-by: David Hildenbrand -- Thanks, David / dhildenb