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[91.12.100.112]) by smtp.gmail.com with ESMTPSA id u8sm8331509wrp.66.2021.04.14.04.54.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 Apr 2021 04:54:18 -0700 (PDT) To: Oscar Salvador , Andrew Morton Cc: Mike Kravetz , Vlastimil Babka , Michal Hocko , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210413104747.12177-1-osalvador@suse.de> <20210413104747.12177-3-osalvador@suse.de> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v7 2/7] mm,compaction: Let isolate_migratepages_{range,block} return error codes Message-ID: <2628d20e-3304-1a0c-5246-cfc2320cce8b@redhat.com> Date: Wed, 14 Apr 2021 13:54:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210413104747.12177-3-osalvador@suse.de> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 825A1130 X-Stat-Signature: uym5fgk1m65h9hzgrm3s5jci7yoj4dpd Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf12; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=216.205.24.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618401256-254964 Content-Transfer-Encoding: quoted-printable 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 13.04.21 12:47, Oscar Salvador wrote: > Currently, isolate_migratepages_{range,block} and their callers use > a pfn =3D=3D 0 vs pfn !=3D 0 scheme to let the caller know whether ther= e was > any error during isolation. > This does not work as soon as we need to start reporting different erro= r > codes and make sure we pass them down the chain, so they are properly > interpreted by functions like e.g: alloc_contig_range. >=20 > Let us rework isolate_migratepages_{range,block} so we can report error > codes. > Since isolate_migratepages_block will stop returning the next pfn to be > scanned, we reuse the cc->migrate_pfn field to keep track of that. >=20 > Signed-off-by: Oscar Salvador > Acked-by: Vlastimil Babka > --- > mm/compaction.c | 54 +++++++++++++++++++++++++++---------------------= ------ > mm/internal.h | 10 ++++++++-- > mm/page_alloc.c | 7 +++---- > 3 files changed, 38 insertions(+), 33 deletions(-) >=20 > diff --git a/mm/compaction.c b/mm/compaction.c > index 8c5028bfbd56..eeba4668c22c 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -787,15 +787,15 @@ static bool too_many_isolated(pg_data_t *pgdat) > * > * Isolate all pages that can be migrated from the range specified by > * [low_pfn, end_pfn). The range is expected to be within same pagebl= ock. > - * Returns zero if there is a fatal signal pending, otherwise PFN of t= he > - * first page that was not scanned (which may be both less, equal to o= r more > - * than end_pfn). > + * Returns errno, like -EAGAIN or -EINTR in case e.g signal pending or= congestion, > + * or 0. > + * cc->migrate_pfn will contain the next pfn to scan (which may be bot= h less, > + * equal to or more that end_pfn). I failed to parse the last sentence -- e.g., using "both" and then=20 listing three options. Also, s/than/than/? Can we simplify to "cc->migrate_pfn will contain the next pfn to scan" > * > * The pages are isolated on cc->migratepages list (not required to b= e empty), > - * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn= field > - * is neither read nor updated. > + * and cc->nr_migratepages is updated accordingly. > */ > -static unsigned long > +static int > isolate_migratepages_block(struct compact_control *cc, unsigned long = low_pfn, > unsigned long end_pfn, isolate_mode_t isolate_mode) > { > @@ -809,6 +809,9 @@ isolate_migratepages_block(struct compact_control *= cc, unsigned long low_pfn, > bool skip_on_failure =3D false; > unsigned long next_skip_pfn =3D 0; > bool skip_updated =3D false; > + int ret =3D 0; > + > + cc->migrate_pfn =3D low_pfn; > =20 > /* > * Ensure that there are not too many pages isolated from the LRU > @@ -818,16 +821,16 @@ isolate_migratepages_block(struct compact_control= *cc, unsigned long low_pfn, > while (unlikely(too_many_isolated(pgdat))) { > /* stop isolation if there are still pages not migrated */ > if (cc->nr_migratepages) > - return 0; > + return -EAGAIN; > =20 > /* async migration should just abort */ > if (cc->mode =3D=3D MIGRATE_ASYNC) > - return 0; > + return -EAGAIN; > =20 > congestion_wait(BLK_RW_ASYNC, HZ/10); > =20 > if (fatal_signal_pending(current)) > - return 0; > + return -EINTR; > } > =20 > cond_resched(); > @@ -875,8 +878,8 @@ isolate_migratepages_block(struct compact_control *= cc, unsigned long low_pfn, > =20 > if (fatal_signal_pending(current)) { > cc->contended =3D true; > + ret =3D -EINTR; > =20 > - low_pfn =3D 0; > goto fatal_pending; > } > =20 > @@ -1130,7 +1133,9 @@ isolate_migratepages_block(struct compact_control= *cc, unsigned long low_pfn, > if (nr_isolated) > count_compact_events(COMPACTISOLATED, nr_isolated); > =20 > - return low_pfn; > + cc->migrate_pfn =3D low_pfn; > + > + return ret; > } > =20 > /** > @@ -1139,15 +1144,15 @@ isolate_migratepages_block(struct compact_contr= ol *cc, unsigned long low_pfn, > * @start_pfn: The first PFN to start isolating. > * @end_pfn: The one-past-last PFN. > * > - * Returns zero if isolation fails fatally due to e.g. pending signal. > - * Otherwise, function returns one-past-the-last PFN of isolated page > - * (which may be greater than end_pfn if end fell in a middle of a THP= page). > + * Returns errno, like -EAGAIN or -EINTR in case e.g signal pending or= congestion, errno is usually positive. > + * or 0. I'd be more specific here. Something like " Returns 0 if isolation succeeded. Returns -EINTR if a fatal signal is=20 pending. Returns -EAGAIN when contended and the caller should retry. In any case, cc->migrate_pfn is set to one-past-the-last PFN that has=20 been isolated. " --=20 Thanks, David / dhildenb