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b=OaR0KTYAHvedbhScdD1MKnXCwZN8HR/UB4CG9w1EFxa9RQXBYPX0va8XjlC5iOwtX LN/6IWqMM58WRi9lUqoBuE7WrkJ7bMGULHINgQ0r27m12oYgbOu/tgCFTWa8rz5gw0 9Mh2g8XpRS+P7fKT6w6eA7TFzppUF5lrce42syUQ= Date: Wed, 26 Feb 2025 14:02:07 -0800 From: Andrew Morton To: Christoph Hellwig Cc: Mike Snitzer , Trond Myklebust , Anna Schumaker , linux-nfs@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH for-akpm for-6.14-rcX] NFS: fix nfs_release_folio() to not call nfs_wb_folio() from kcompactd Message-Id: <20250226140207.90cc614ca22db560f19638ca@linux-foundation.org> In-Reply-To: References: <20250225003301.25693-1-snitzer@kernel.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 99B928000C X-Rspamd-Server: rspam08 X-Rspam-User: X-Stat-Signature: fp7r3ydtiz3ywaotnah748zbdypscqbr X-HE-Tag: 1740607329-929288 X-HE-Meta: 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 I1O5ZGKM CbZl45nM80i08/677+9loIoltPBPuOOFIK9322o2oDOd4i4TcgfyMFsRBbanQy98n+vSTTTfLIMUS47DqAifKRGDAOlLc7fSMgNmaafB7gLz6kqbXuBWEaclGTHZwe7vXbwIg4zpywpA5EHWH5Bm7FwX9Gke05Q08GHcJkWWjoB6ub1ln2JnMq70yix6ONGL+pnCSzxKus8tLp07EM6ELHQjvkJHK35pPaksKvtAhM8upwBBE5I/G8++wfdhtCMp7RABs7MPJ5Qg+sEgXT/6lAl5aHNAFRQj51Ic9QCftGuV/vLoIV+G2vGtX+qW/HPzZfJqzMWTY+Vu5uK/xopL3nqVDSuq7wH7PxpnQ 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, 26 Feb 2025 06:58:11 -0800 Christoph Hellwig wrote: > On Mon, Feb 24, 2025 at 07:33:01PM -0500, Mike Snitzer wrote: > > Add PF_KCOMPACTD flag and current_is_kcompactd() helper to check for > > it so nfs_release_folio() can skip calling nfs_wb_folio() from > > kcompactd. > > > > Otherwise NFS can deadlock waiting for kcompactd enduced writeback > > which recurses back to NFS (which triggers writeback to NFSD via > > NFS loopback mount on the same host, NFSD blocks waiting for XFS's > > call to __filemap_get_folio): > > Having a flag for a specific kernel thread feels wrong. Why do you think this? We are getting a bit short of space in tsk->flags. Five PF__HOLE__'s remain. For this patch and for kswapd I guess we could simply record the task_struct*'s in a static array, something like static struct task_struct nice_name[max nodes]; ... if (current == nice_name[my node]) ... It's something we can look at if we start getting really tight on PF_ space.