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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pdEGA-00G5od-Cn; Fri, 17 Mar 2023 17:52:58 +0000 Date: Fri, 17 Mar 2023 17:52:58 +0000 From: Matthew Wilcox To: Mike Kravetz Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: THP backed thread stacks Message-ID: References: <20230306235730.GA31451@monkey> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230306235730.GA31451@monkey> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 88E9DA000B X-Rspam-User: X-Stat-Signature: f4dfoozt7axtxonamsq7mh64tfwtacs5 X-HE-Tag: 1679075581-204068 X-HE-Meta: U2FsdGVkX19oBMoJgxYsnOM1JHblEnq01t7MnI6RT7p+Jw0OhRkb7YGUHkIWyQY1bN3hLbrHyh6i9QbSHpWQaVQBe9zHmb+b1n3K0VA7NJlZt/mibVR88gtyIQ/HMUxZx2UuyLksxt2vIogcEE19PMhV8Ww6pHhiuLeQupdQfJzafMnMwAltMl+cXDyyORyWKUyyb5Te5arcmlapyPe+Pk7ohiYniDZcvGx1GKQUcBEAUkzvP6OhRzvoq+SGa5MGlYoeAFPuizJRGDkh3SsV6PzjCTAUlceSDFophCVwEgTEcoAD7YzG3Njxu7vdLxrHxY2Qmr2vyJcVj41yD+7qfXXylgd8puRy81n8CHuI2TjD2ef4sjfQZABL/CAXKzcSpg6J0rWM0B+pN3qkEPesyvj5TwlACJxOFJvpKy/WJ3P1dfv77e11kTGbQFY5MG6Q+09ExE3oRhpdVzKNbKiLO5fOfOwM6GBnOG7PTMOVJ40tW7cMlPn8SEZUvUuohBEXxev0yE+KkRD8Oy97Z/M8IzDyAZLj+WY0JMjd9Y6qtuyGYmzvDnG12UVMWcb60SqqRjcfwysEIgfO0SHQr9ipzYvgBQMGFfezeYDz7gsWsXmj5OIkjdEdgHmqjXsajCGmXe0nQG5J6ingGOUrOBi6UKOdeHMGT2sps6hM3e3xFLrg8/ZCKzxMxEW21TIcsGkFSsAY5RLq/zfD1e7pvmVufWYl7vh/FFvVFVItnossXOCrhZz9D5DGDG+Wnds36Q1sQNQZ1EpLQn0BagJAUo45d/G50xm8byG3Swqwd7myR1TEOxQq7rTyt2MZpFWCc4S/OBPArL23OL9wqpPnTCboj6TNQ0mHCQ87Hvp5yYqS1+ORLIhtIjM+PEvcsM6e06wUuosl/xPI4UlNUrI6TqcuR9SebOgXxGY9OjkNgMHS9aW5rqyEnZMvSksP36auhi952omZKBg+h3dEFjWWBy4 VVUgAP8T OwmOlO+MBERt2xYY8uL9HeQuYJOy7npOCVfM2sgvuy1+Yo1Llr766sNnpRwNMCaD3e8Fpg6pgwoPJQKk/KuuiV8lLVmOeFizgJGSG100Lgm5ru4zoq0luaThYUKtfmSzPkKgP2/l9DUmauxACGpk+8hOJaA== 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: On Mon, Mar 06, 2023 at 03:57:30PM -0800, Mike Kravetz wrote: > One of our product teams recently experienced 'memory bloat' in their > environment. The application in this environment is the JVM which > creates hundreds of threads. Threads are ultimately created via > pthread_create which also creates the thread stacks. pthread attributes > are modified so that stacks are 2MB in size. It just so happens that > due to allocation patterns, all their stacks are at 2MB boundaries. The > system has THP always set, so a huge page is allocated at the first > (write) fault when libpthread initializes the stack. Do you happen to have an strace (or similar) so we can understand what the application is doing? My understanding is that for a normal app (like, say, 'cat'), we'll allow up to an 8MB stack, but we only create a VMA that is 4kB in size and set the VM_GROWSDOWN flag on it (to allow it to magically grow). Therefore we won't create a 2MB page because the VMA is too small. It sounds like the pthread library is maybe creating a 2MB stack as a 2MB VMA, and that's why we're seeing this behaviour?