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charset="iso-8859-1" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: d2ee4345-4bd0-4295-5ff5-08d74b7d8d8a X-MS-Exchange-CrossTenant-originalarrivaltime: 07 Oct 2019 23:24:52.0581 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: FTmMd1D1g8/FpZIF5kk8hBSuvhgi3KavxN7onYhrjO6ZyM1OJIgRJn3Fl9Z2wXDA X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN8PR15MB2947 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,1.0.8 definitions=2019-10-07_04:2019-10-07,2019-10-07 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 priorityscore=1501 mlxlogscore=741 clxscore=1015 spamscore=0 phishscore=0 bulkscore=0 impostorscore=0 suspectscore=0 mlxscore=0 adultscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1908290000 definitions=main-1910070209 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 07, 2019 at 06:19:26PM +0200, Michal Koutn=FD wrote: > On Fri, Oct 04, 2019 at 03:11:04PM -0700, Roman Gushchin wr= ote: > > An inode which is getting dirty for the first time is associated > > with the wb structure (look at __inode_attach_wb()). It can later > > be switched to another wb under some conditions (e.g. some other > > cgroup is writing a lot of data to the same inode), but generally > > stays associated up to the end of life of the inode structure. > What about dissociating the wb structure from the charged cgroup after > the particular writeback finished? (I understand from your description > that wb structure outlives the dirtier and is kept due to other inode > (read) users, not sure if that's correct assumption.) Well, that sounds nice, and I thought into this direction, but I've no idea how to implement it :) First, it's hard to find a good moment for dissociation. It seems that the good moment is after the cgroup has been removed by the user and most of the dirty memory has been written back, but it's hard to formalize, given that other cgroups may write to the same inode concurrently. Second, the current code assumes that wb->memcg association never breaks, and it's not that trivial to get rid of this assumption without introducing new locks, etc. Thanks!