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Mon, 14 Dec 2020 23:10:45 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0BEN58bf096736; Mon, 14 Dec 2020 23:10:44 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserp3030.oracle.com with ESMTP id 35d7em461d-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 14 Dec 2020 23:10:44 +0000 Received: from abhmp0017.oracle.com (abhmp0017.oracle.com [141.146.116.23]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 0BENAhq1002957; Mon, 14 Dec 2020 23:10:43 GMT Received: from dhcp-10-159-135-62.vpn.oracle.com (/10.159.135.62) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 14 Dec 2020 15:10:43 -0800 Subject: Re: [PATCH RFC 0/8] dcache: increase poison resistance To: Konstantin Khlebnikov Cc: Konstantin Khlebnikov , Linux Kernel Mailing List , linux-fsdevel , linux-mm@kvack.org, Alexander Viro , Waiman Long , Gautham Ananthakrishna , matthew.wilcox@oracle.com References: <158893941613.200862.4094521350329937435.stgit@buzz> <97ece625-2799-7ae6-28b5-73c52c7c497b@oracle.com> From: Junxiao Bi Message-ID: <04b4d5cf-780d-83a9-2b2b-80ae6029ae2c@oracle.com> Date: Mon, 14 Dec 2020 15:10:25 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9835 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 spamscore=0 bulkscore=0 suspectscore=0 adultscore=0 mlxscore=0 mlxlogscore=999 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012140154 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9835 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 mlxlogscore=999 impostorscore=0 lowpriorityscore=0 clxscore=1015 spamscore=0 malwarescore=0 priorityscore=1501 phishscore=0 mlxscore=0 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012140154 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 12/13/20 11:43 PM, Konstantin Khlebnikov wrote: > > > On Sun, Dec 13, 2020 at 9:52 PM Junxiao Bi > wrote: > > On 12/11/20 11:32 PM, Konstantin Khlebnikov wrote: > > > On Thu, Dec 10, 2020 at 2:01 AM Junxiao Bi > > > >> > wrote: > > > >=C2=A0 =C2=A0 =C2=A0Hi Konstantin, > > > >=C2=A0 =C2=A0 =C2=A0We tested this patch set recently and found it= limiting negative > >=C2=A0 =C2=A0 =C2=A0dentry > >=C2=A0 =C2=A0 =C2=A0to a small part of total memory. And also we d= on't see any > >=C2=A0 =C2=A0 =C2=A0performance > >=C2=A0 =C2=A0 =C2=A0regression on it. Do you have any plan to inte= grate it into > >=C2=A0 =C2=A0 =C2=A0mainline? It > >=C2=A0 =C2=A0 =C2=A0will help a lot on memory fragmentation issue = causing by > dentry slab, > >=C2=A0 =C2=A0 =C2=A0there were a lot of customer cases where sys% = was very high > since > >=C2=A0 =C2=A0 =C2=A0most > >=C2=A0 =C2=A0 =C2=A0cpu were doing memory compaction, dentry slab = was taking too > much > >=C2=A0 =C2=A0 =C2=A0memory > >=C2=A0 =C2=A0 =C2=A0and nearly all dentry there were negative. > > > > > > Right now I don't have any plans for this. I suspect such > problems will > > appear much more often since machines are getting bigger. > > So, somebody will take care of it. > We already had a lot of customer cases. It made no sense to leave s= o > many negative dentry in the system, it caused memory fragmentation > and > not much benefit. > > > Dcache could grow so big only if the system lacks of memory pressure. > > Simplest solution is a cronjob=C2=A0which provinces=C2=A0such pressure = by > creating sparse file on disk-based fs and then reading it. > This should wash away all inactive caches with no IO and zero chance=20 > of oom. Sound good, will try. > > > > > First part which collects negative dentries at the end list of > > siblings could be > > done in a more obvious way by splitting the list in two. > > But this touches much more code. > That would add new field to dentry? > > > Yep. Decision=C2=A0is up to maintainers. > > > > > Last patch isn't very rigid but does non-trivial changes. > > Probably it's better to call some garbage collector thingy > periodically. > > Lru list needs pressure to age and reorder entries properly. > > Swap the negative dentry to the head of hash list when it get > accessed? > Extra ones can be easily trimmed when swapping, using GC is to redu= ce > perf impact? > > > Reclaimer/shrinker scans denties=C2=A0in LRU lists, it's an another lis= t. Ah, you mean GC to reclaim from LRU list. I am not sure it could catch=20 up the speed of negative dentry generating. Thanks, Junxiao. > My patch used order in hash lists is a very unusual way. Don't be=20 > confused. > > There are four lists > parent - siblings > hashtable - hashchain > LRU > inode - alias > > > Thanks, > > Junxioao. > > > > > Gc could be off by default or thresholds set very high (50% of > ram for > > example). > > Final setup could be left up to owners of large systems, which > needs > > fine tuning. >