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Tue, 2 Sep 2025 07:22:23 -0400 (EDT) Date: Tue, 2 Sep 2025 12:22:21 +0100 From: Kiryl Shutsemau To: "Pankaj Raghav (Samsung)" Cc: David Hildenbrand , Ryan Roberts , Lorenzo Stoakes , Baolin Wang , Dev Jain , Barry Song , Andrew Morton , Nico Pache , Zi Yan , "Liam R . Howlett" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, willy@infradead.org, mcgrof@kernel.org, gost.dev@samsung.com, Pankaj Raghav Subject: Re: [PATCH] huge_memory: return -EINVAL in folio split functions when THP is disabled Message-ID: References: <20250902084036.208921-1-kernel@pankajraghav.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250902084036.208921-1-kernel@pankajraghav.com> X-Rspamd-Queue-Id: A20631C0004 X-Rspam-User: X-Stat-Signature: jx8ixfomz6mx6ydxp5e449pjjwh5hkir X-Rspamd-Server: rspam09 X-HE-Tag: 1756812146-359103 X-HE-Meta: U2FsdGVkX19s5sE8MeBEXVvhA1OsRC4wrEuXv1LbImoEqHgM6wcctJrge1DSeRFN1KE293bvF+huzawiETYPA2uPHLFV4rLyDhu9JhC+GSHrsi9kKmQkCa+U7DLaoILfS6N/n9rYijbSE6A/1V3IHEMycaWfnMvaMf0UBxa7DoQdSqmaa0U0cokYGEzmXuLXqG0RpUluJAavxgG87ZVSbpSyMl7dWjqKXPnSXwsjmyXEsv8EESK/CxZeY5OKIkPjTUA1R9E+NKFbHEEJwJD3llXmUQoManZIFoECvFOj5bvFgFCxccHakoEKQcx0N589fTPORHFM3578UQhIRp8eSGsXU3IRYZ+tQnGv8QNRdCBX4DYlCjevltGI/TvNcyXTBoTtYhHuZLWT59WvTR0dpeH9pMiq/cwWBVfZhBqWRFdUAjrSYtSuDty+a11iKsIXIlEX5ZXYXckMOl11y5PH7tPcb9c0DHBWWoAt58SS0x3na3wN6xYnObr3VVi60eHt+mjLpr2WmDFAt9bK9v0fso7czJmIiVlwNz6OW0JUjSp5mTaf9fJ2A0h8EGzxbgDKQ2s7y4wy5rEp6z7swQntPlvwAj7H8Y0L3ne+jfMWvU20Q4yAIwedSN4UTqVHCvyGcBgsaQUkcPfFLfqnDliH4HCAtX7xp/HzpSP23c3mKR8dHVqoDUbjgF7VuuiISv68BuN4+icxs9BV5Ih1CbzsYjo1b5YttRVfbtGGqza/LgF0omLW12PWn8GBnexokqDUaYEzGuds9TdSAhlBOZ1yfoROGn/+g4QXqSSi+qqlqnarWrlyzz2F+HLAdJWpDuEJ+tM9zr/FKuaF5JZRd2XKdvv7TLVoBdYlAOTEufRd6/5hBSq25SH2pJMPcnUvLHOf5dHVRux3hlzxuutnNu+MgW41/p6LXSZ7DZIBW1UDiuT2uHg6fcY8y15xqYmr4+HU2HtLCjWfczYMtps3ypN LPCLQcPb 9bf9B17/FuLkB6kXTT85fsQG1AhaaIfTOsKKbveYB0loAMsXOF2FxGe5/6dJgbjJlWo9Hn8LItknnGyJwEkwCdIEVy1tAUBTpYsa4kAG3VtQduMaoRnJ/mOY2Zwxeo0nOKR7wl89BEu3kLlxtEtr94gwdngtkOKkQKcXzniZfAW/GVu3Thadl7B3rQR2Ylm/3AJFy1zgkXvCYn0y6RdGl8m873gIN6rGGeVPIFmt4o588/w31gB6tq67JnWgjFhC+8eSsOpTegDrusIrWW9NjWwqLsIj2L5G7krIZdxURHGhA252kKLpegza2tFmlg8H6vc1sbv7YdhofmL58Pj3+potXgJpTE7Mjr3MilAQDE5CAhmBj0hq0nowJbTHTKUkmA60YD+Ne8zjLnm8iGMlinDbznIMppzt+u5gTFSTXZJSSZHZDwSvnUa8npw== 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 Tue, Sep 02, 2025 at 10:40:36AM +0200, Pankaj Raghav (Samsung) wrote: > From: Pankaj Raghav > > split_huge_page_to_list_[to_order](), split_huge_page() and > try_folio_split() return 0 on success and error codes on failure. > > When THP is disabled, these functions return 0 indicating success even > though an error code should be returned as it is not possible to split a > folio when THP is disabled. Other view is that the page is already split therefore nop. > Make all these functions return -EINVAL to indicate failure instead of > 0. > > This issue was discovered while experimenting enabling large folios > without THP and found that returning 0 in these functions is resulting in > undefined behavior in truncate operations. This change fixes the issue. Could you elaborate on the undefined behaviour? I don't see it. If you argue that this code should not be reachable on !THP config, add WARN() there. But I don't see a value. -- Kiryl Shutsemau / Kirill A. Shutemov