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b=swC7I8sHM52a/RUTuobaO6U2Z4PX35vJoB46A8XLLwChLLWdb+tjlShuHSqhLQq/B 3lJAyXE2QD23pkR+FfzBmPgbomh2ciDvXhc3eqHLuJ76BcmmIRLytZA6MWtU5Q0LVp fg8Jt7Ecc9lQGppPfBliHnBE7PK8ug2SG3MSgpKU= Date: Tue, 7 Oct 2025 15:34:24 -0700 From: Andrew Morton To: Roman Gushchin Cc: linux-kernel@vger.kernel.org, "Matthew Wilcox (Oracle)" , Jan Kara , Dev Jain , linux-mm@kvack.org Subject: Re: [PATCH v3] mm: readahead: make thp readahead conditional to mmap_miss logic Message-Id: <20251007153424.1b46a4018e17d5dafd7fb126@linux-foundation.org> In-Reply-To: <20251006175106.377411-1-roman.gushchin@linux.dev> References: <20251006175106.377411-1-roman.gushchin@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (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-Stat-Signature: qgxizfbadbcyqwic6pz7yg9cwbw7kjcz X-Rspamd-Queue-Id: 592B28000B X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1759876466-918145 X-HE-Meta: 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 sbh58wrA PSYVepZP60oi9mpikPNDRGoL6W68e2qAbrbiLMdE/7RqkJWLyvu8vWth0I+ICaMZXCz+P/gua1WmdnSzpWwIiPwXEIq+nXAsPERrUghRuM25Srq2QZ63C7mLszVzaWxcnjdhT8RCE8Na5LX96GYZOCAGh90M/NzDn8KSIq+gq5B1NZik0f9PfUql4Qu7m+21+0MPJ3omhahRkPDnJ14KVIfwQSmh0NZxdZYfvmxaa4R3uq3sopKcaY+/GLX8/5Gn/cg+lVC6LPllDhAp/dsfX/SYnkiNmoP763vbKfz/Q6ij5PD9jRcFVJmzr78bND2SipLu1fhQZt9Zev7jOAWOK+ar9d0mrMshpufrkQeFFKFw/5ttux09YlRYd4/0wfkIV9bT5Q/sM4qa8uafz82k+3TdH06zaZc5GPqWt 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 Mon, 6 Oct 2025 10:51:06 -0700 Roman Gushchin wrote: > Commit 4687fdbb805a ("mm/filemap: Support VM_HUGEPAGE for file mappings") > introduced a special handling for VM_HUGEPAGE mappings: even if the > readahead is disabled, 1 or 2 HPAGE_PMD_ORDER pages are > allocated. Three years ago. > This change causes a significant regression So no backport suggested? I guess reasonable given how long 4687fdbb805a has been in tree. > > ... > > for containers with a > tight memory.max limit, if VM_HUGEPAGE is widely used. Prior to this > commit, mmap_miss logic would eventually lead to the readahead > disablement, effectively reducing the memory pressure in the > cgroup. With this change the kernel is trying to allocate 1-2 huge > pages for each fault, no matter if these pages are used or not > before being evicted, increasing the memory pressure multi-fold. > > ... > > Signed-off-by: Roman Gushchin > Cc: Matthew Wilcox (Oracle) > Cc: Jan Kara > Cc: Dev Jain But I'll slap the Fixes: in there, it might help someone.