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[34.78.232.44]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-390cd8e7121sm2514621f8f.61.2025.02.25.06.41.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Feb 2025 06:41:01 -0800 (PST) Date: Tue, 25 Feb 2025 14:40:57 +0000 From: Brendan Jackman To: Vlastimil Babka Cc: Johannes Weiner , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] mm: page_alloc: don't steal single pages from biggest buddy Message-ID: References: <20250225001023.1494422-1-hannes@cmpxchg.org> <20250225001023.1494422-2-hannes@cmpxchg.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Feb 25, 2025 at 03:35:25PM +0100, Vlastimil Babka wrote: > >> - return NULL; > >> + if (alloc_flags & ALLOC_NOFRAGMENT) > >> + return NULL; > > > > Is this a separate change? Is it a bug that we currently allow > > stealing a from a fallback type when ALLOC_NOFRAGMENT? (I wonder if > > the second loop was supposed to start from min_order). > > It's subtle but not a new condition. Previously ALLOC_NOFRAGMENT would > result in not taking the "goto find_smallest" path because it means > searching >=pageblock_order only and that would always be can_steal == true > if it found a fallback. And failure to find fallback would reach an > unconditional return NULL here. Now we fall through the search below > (instead of the goto), but ALLOC_NOFRAGMENT must not do it so it's now > explicit here. Ahhhh yes, thank you for the help. The new explicit code is much better. Reviewed-by: Brendan Jackman