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From: Shakeel Butt To: Joanne Koong Cc: miklos@szeredi.hu, linux-fsdevel@vger.kernel.org, jefflexu@linux.alibaba.com, josef@toxicpanda.com, linux-mm@kvack.org, bernd.schubert@fastmail.fm, kernel-team@meta.com Subject: Re: [PATCH v4 1/6] mm: add AS_WRITEBACK_MAY_BLOCK mapping flag Message-ID: References: <20241107235614.3637221-1-joannelkoong@gmail.com> <20241107235614.3637221-2-joannelkoong@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241107235614.3637221-2-joannelkoong@gmail.com> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: EF38A14000C X-Rspamd-Server: rspam11 X-Stat-Signature: ridau5bd9ojt5a4n4se8j64s1mcq8tku X-HE-Tag: 1731111020-402900 X-HE-Meta: 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 I3Mj7BtE 8vort15SdDPyi8ZTtLStVr8LCDVLdBkaFg/88L+ANcJxJRxg3aOhFyGsECxyhOOKXMn5Tbq4U5pzh+5mMu0LWRxDKXvNISPvXTivPWD2yMO/DP4GlLBuK4ep+0T2cnpZ4dE0ME8I2ZtHhXDRgU5nogygPbphKwJeo06M2bfz/fzrj35r9p6GSt2ec4+lsaA1YRZf8oDggPf7lS8OdQo0BmZ5sIQ== 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 Thu, Nov 07, 2024 at 03:56:09PM -0800, Joanne Koong wrote: > Add a new mapping flag AS_WRITEBACK_MAY_BLOCK which filesystems may set > to indicate that writeback operations may block or 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 > --- > include/linux/pagemap.h | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index 68a5f1ff3301..eb5a7837e142 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -210,6 +210,7 @@ enum mapping_flags { > AS_STABLE_WRITES = 7, /* must wait for writeback before modifying > folio contents */ > AS_INACCESSIBLE = 8, /* Do not attempt direct R/W access to the mapping */ > + AS_WRITEBACK_MAY_BLOCK = 9, /* Use caution when waiting on writeback */ To me 'may block' does not feel right. For example in reclaim code, folio_wait_writeback() can get blocked and that is fine. However with non-privileged fuse involved, there are security concerns. Somehow 'may block' does not convey that. Anyways, I am not really pushing back but I think there is a need for better name here. > /* Bits 16-25 are used for FOLIO_ORDER */ > AS_FOLIO_ORDER_BITS = 5, > AS_FOLIO_ORDER_MIN = 16, > @@ -335,6 +336,16 @@ static inline bool mapping_inaccessible(struct address_space *mapping) > return test_bit(AS_INACCESSIBLE, &mapping->flags); > } > > +static inline void mapping_set_writeback_may_block(struct address_space *mapping) > +{ > + set_bit(AS_WRITEBACK_MAY_BLOCK, &mapping->flags); > +} > + > +static inline bool mapping_writeback_may_block(struct address_space *mapping) > +{ > + return test_bit(AS_WRITEBACK_MAY_BLOCK, &mapping->flags); > +} > + > static inline gfp_t mapping_gfp_mask(struct address_space * mapping) > { > return mapping->gfp_mask; > -- > 2.43.5 >