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AJvYcCW5OZtXlZ2naRcPdPEInIuAQ5+yqj0IMYo46esd9m/+7qQMMgppfo7D4LFvrMF6YRn3odiV+mDlzA==@kvack.org X-Gm-Message-State: AOJu0Yy5KxoRT5ipn7QpTlkFm+T6c+Kt/YeNDBzNBhCKtzO+DVpAFAtF B7xkXZgoXU9Omvm0fEw1G4+8cinTwMvv6UcPQb1YLvP3m5eKJttLdABvj+3+kWh5OrPlbE7Sv7i dOSo3NkCPmAp67fQn/Yn0wJi/QCY= X-Gm-Gg: ASbGncvCg1g1w5kGDPU5mMOSUOOEJzPyKPy6YgRlnl2kUISYPk7G1mIORs9WXf14S+6 3IbftxZlYGItSQ491t+ABWbcv1FhAFC8dKf7jBU/m4+COXDx5pM9of9ejpnM8GW0H74UThF6bY1 mF8GGWJbAzZk3AIQXWfx7PO9koCZbmJbpwwt5B2lu5pA== X-Google-Smtp-Source: AGHT+IFSQt7s2S3diZ6GEacLNQ3FK+Pn8kzzfoPCdjBaS9N90hjojGsbBGWs8cv9KnEJVglznxGfKDwZ7TSQmxR0eTc= X-Received: by 2002:a05:620a:2903:b0:7c5:6ef2:2767 with SMTP id af79cd13be357-7c7759eab20mr492729085a.2.1743797370803; Fri, 04 Apr 2025 13:09:30 -0700 (PDT) MIME-Version: 1.0 References: <20250404181443.1363005-1-joannelkoong@gmail.com> <20250404181443.1363005-2-joannelkoong@gmail.com> <0462bb5b-c728-4aef-baaf-a9da7398479f@redhat.com> In-Reply-To: <0462bb5b-c728-4aef-baaf-a9da7398479f@redhat.com> From: Joanne Koong Date: Fri, 4 Apr 2025 13:09:19 -0700 X-Gm-Features: ATxdqUGOpEdH6-QzzD09W4OCfRX_Obt5ojK2E8RLlQdnPHV74MxPE0Rx6EKOYvk Message-ID: Subject: Re: [PATCH v7 1/3] mm: add AS_WRITEBACK_INDETERMINATE mapping flag To: David Hildenbrand Cc: miklos@szeredi.hu, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, jefflexu@linux.alibaba.com, shakeel.butt@linux.dev, bernd.schubert@fastmail.fm, ziy@nvidia.com, jlayton@kernel.org, kernel-team@meta.com, Miklos Szeredi Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: D26B440006 X-Stat-Signature: wfoa1sord6m4y4onq5hoidbhc6y3bqqz X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1743797371-13108 X-HE-Meta: U2FsdGVkX1+S9F9ezvaarogtNJEXY+F6tqYtZgHeFRKoOVXuRs12MoVkHQZuxm48ZKwSUVmR5WR7Zy1ZZumxTmdEaQ3OwOXRUrF5b+x10442cyfAAP/hrJ5zO7YFNlk9UInhpTexocxd2GFmqLT2mgBB0qcOV0pJhXC5pty8/8GUBlftBzLnP02AfoEffbHVVAeZpzzJnGkLDp61SPkUH+m0uqgedXSyPhetvrtlIhc4RaUbJdowzpQkNvDUzC4EPvoq4SznO/hu8cF+7r8YXycoM3DJLi/G3bz+oTC139n2IFo/p+wM8ekARXTOixWpnBkz+vxEX9fPi+UptjW3MV4MzMosdFC88tFMBwDTeQYRhgBSkIvZmV312gI/KFceor4Jych70Igj5fbXvuOetE0ReV5Tn/U2HRScUtj/azgc15qJQBNypjOvUDG5oqTvp4LHLklH3pCw4RZSRkuqhzxwHkL0F4dnkkRkgySU0dkwEn9e+PPFAaBcu8LWxmUwDgafGTAp2KU5lst1oMyrlrhwYumsrpF3nX6DvUM1JKTCXQlbC/HfmQitOmTMoEkc1sR14+l7j4d4Sf/T3HYKf3zVw/ovWhDJItEpHAVS6R4lhSHb+XBNq6lJ+cn/IOB9ZGF/O26uslBerVQJYOZrBVl680d4ee9sILOTyr5z8+lF6mHVBtYi/ZkSEe3PRj9ylPc8Iv7Jn8O4Gy3Llw/jtdR34RQF9wEu0uVzb7CnUCuXptz/jttGvI9DB1+FbIUH8/9V7NnMSWW1wJxX2gyFVHOM1a8BH/h/0ebXEbY/uVgvGggScYxGA2S8jTsCLUPnUt2gVjEacQKDSbXF3/cQ2Z1zI9/db5AWL2oLSYKpl24EMaZVNn6yHlSCaqNyXaz46MqqDGJmlKqDHeMdIURAilqAvpuv1y3qC1VK7CKnK7/1mzy7a26oNfLY0RIekkaRtVLCPmXhUbz4SGEbpSh GsVUaEgH iVFji7vHaQGt2WnhAdvYlyly5HWt9tN/+dzwBqrSfSNNvxKL5CJWdGCda7duhx/h7brgA9PlMNzoaSxQ/+q6sl8vvCR7x8HcoGam0nEeyZdwwPpsrT/NC4EzSraVQMLaAFf4Ud2mx+SGNZcQxEI/XOlWfCFsCvJZShlZpJmV9Lt1U3S6hGKrZql1XdhhitsJZcy0pgFkNI1P2xawBEa+69zwBdpOE/mnBC763Rz55kLX/hPH0u91ndtpTACSSqGk7EZZVCaQc0VX9QCG9V1Ld4unsTI/XsYjTBLUY+aD48yvVBIh8OsPGQ5GfaKfciOQjunK/us17Y8gHzaQs5AnMu45vFHdBsHrM861ZglITuBDoD5eWDbilV4SAEn2PYZiWDErZAebZV83vA0jqJrVeQnsdeSP9tPNSMeKvLZKBjw1S+j4NFlFZC3EMhQ== 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: List-Subscribe: List-Unsubscribe: On Fri, Apr 4, 2025 at 12:13=E2=80=AFPM David Hildenbrand wrote: > > On 04.04.25 20:14, Joanne Koong wrote: > > Add a new mapping flag AS_WRITEBACK_INDETERMINATE which filesystems may > > set to indicate that writing back to disk may take an indeterminate > > amount of time to complete. Extra caution should be taken when waiting > > on writeback for folios belonging to mappings where this flag is set. > > > > Signed-off-by: Joanne Koong > > Reviewed-by: Shakeel Butt > > Acked-by: Miklos Szeredi > > --- > > include/linux/pagemap.h | 11 +++++++++++ > > 1 file changed, 11 insertions(+) > > > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > > index 26baa78f1ca7..762575f1d195 100644 > > --- a/include/linux/pagemap.h > > +++ b/include/linux/pagemap.h > > @@ -210,6 +210,7 @@ enum mapping_flags { > > AS_STABLE_WRITES =3D 7, /* must wait for writeback before modif= ying > > folio contents */ > > AS_INACCESSIBLE =3D 8, /* Do not attempt direct R/W access to = the mapping */ > > + AS_WRITEBACK_INDETERMINATE =3D 9, /* Use caution when waiting on = writeback */ > > /* Bits 16-25 are used for FOLIO_ORDER */ > > AS_FOLIO_ORDER_BITS =3D 5, > > AS_FOLIO_ORDER_MIN =3D 16, > > @@ -335,6 +336,16 @@ static inline bool mapping_inaccessible(struct add= ress_space *mapping) > > return test_bit(AS_INACCESSIBLE, &mapping->flags); > > } > > > > +static inline void mapping_set_writeback_indeterminate(struct address_= space *mapping) > > +{ > > + set_bit(AS_WRITEBACK_INDETERMINATE, &mapping->flags); > > +} > > + > > +static inline bool mapping_writeback_indeterminate(struct address_spac= e *mapping) > > +{ > > + return test_bit(AS_WRITEBACK_INDETERMINATE, &mapping->flags); > > +} > > + > > static inline gfp_t mapping_gfp_mask(struct address_space * mapping) > > { > > return mapping->gfp_mask; > > Staring at this again reminds me of my comment in [1] > > " > b) Call it sth. like AS_WRITEBACK_MIGHT_DEADLOCK_ON_RECLAIM to express > that very deadlock problem. > " > > In the context here now, where we really only focus on the reclaim > deadlock that can happen for trusted FUSE servers during reclaim, would > it make sense to call it now something like that? Happy to make this change. My thinking was that 'AS_WRITEBACK_INDETERMINATE' could be reused in the future for stuff besides reclaim, but we can cross that bridge if that ends up being the case. Will submit v8 with this changed to AS_WRITEBACK_MIGHT_DEADLOCK_ON_RECLAIM. Thanks, Joanne > > [1] > https://lore.kernel.org/linux-mm/0ed5241e-10af-43ee-baaf-87a5b4dc9694@red= hat.com/ > > -- > Cheers, > > David / dhildenb >