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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rfXyW-000000075HY-3ENI; Thu, 29 Feb 2024 04:24:52 +0000 Date: Thu, 29 Feb 2024 04:24:52 +0000 From: Matthew Wilcox To: Kent Overstreet Cc: Amir Goldstein , paulmck@kernel.org, lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-fsdevel , Jan Kara Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC] Reclamation interactions with RCU Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: DABF9120006 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: gnmbnnezh3p9hngsykg6rz3rrb4h17on X-HE-Tag: 1709180701-699734 X-HE-Meta: U2FsdGVkX19T+0rbaJlOzYt93GoMoSpxL7gtYSmnCOxe77T+GdbWJd0hvhVzDgrOTfVlru5fXilIbZ/4QoO8chVpLHLSqvdcuCOPqqFKLvyIiW1BzqurPN7TnkeFhtwrEssx+PkFFpvejHAAe39nwmLdhhdfScNKAv+HTqMCTyH2xb4LL2R09bwK07xy8AFGAnv8d6EoqxIymQ1uC7n+8ss8gR/Z9D/qwydWaDBY4RDkUT49pLey1LcSNSapQ393qTmCXFzvkutz1vQBe+0lU9GXGHPu3o5Mc0K94TbbELJlTVh5HSsfEwFoGp6d8m/jugxiRUHDjuHR3JshYRd1j4Nj9SAXxiGCCbejQgSuywr4qZZCiy1rwkx6XRi/DwcjNRzpkLdF37OI5ZPvKp5XL2PkX4XXdYkMhiHJA07+R1xH19gfzPebtRf0L3XLynn6J/+4c+QFBywG3UNS0klJEJC+p72tNwuxK9Xgs2J67EHpHxtmlGtm9+DGEd2UzhDUbnFVYItiozMvxjZBtS2cZrStLmJ60lgHkcs22GTw/Hb42M0kvCX0//UHG9doK8igjVWFd6UGcV1j0Vue7Yw2hLoibJAMpWc4MjF+yZne8ZTcds7Mv3nOOKXQWA7NxyHbZnIEgFQ0YvPAgW/peJ5/Rk0EDXTL+zOOR+A2Mo3x0K+NJ7rADOwZtCTiCol6R5yNfjAgj8axlGvF86aguDNMmioKtQ240g8bLiGWyaTBUlw/6YKHYxAq83+wGS6QRTA4XGwJnA/WGsqfwXobmn3oWkQKLDRhki0JnetWFQ2ofxeS9pwClGnFl4womV7wPmm9UEnbdG4jiZfD2w3RCkE2xg== 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 Wed, Feb 28, 2024 at 11:17:33PM -0500, Kent Overstreet wrote: > On Wed, Feb 28, 2024 at 07:37:58PM +0000, Matthew Wilcox wrote: > > Perhaps broaden this slightly. On the THP Cabal call we just had a > > conversation about the requirements on filesystems in the writeback > > path. We currently tell filesystem authors that the entire writeback > > path must avoid allocating memory in order to prevent deadlock (or use > > GFP_MEMALLOC). Is this appropriate? It's a lot of work to assure that > > writing pagecache back will not allocate memory in, eg, the network stack, > > the device driver, and any other layers the write must traverse. > > Why would you not simply mark the writeback path with > memalloc_nofs_save()? It's not about preventing recursion, it's about guaranteeing forward progres. If you can't allocate a bio, you can't clean memory.