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b=Ykja3++fMvsuCuwWPyt07z6i+EEmqKxSXXP6uXHoppDRPFaM8aq2/6e4KtCYKtD7H slWahvtljCxDsivxbPDgjyTLfP4ZdVEiM8sDyI/IcwJ3Jp4SBDAVhO6yq0gMjnCATt GMkD4wfwFzlDKPuiXj+9IyspFjfGak8yOlmTpc+9j44cVxco5s2HapzK6iRnw3aRaN 9Ud5Yhd150GM9K3zYbJHLw+YlKlM3ui6SnNG8O++MwfrbFosqm9fYMh9bpzbMrJxOm nambFu4niAlcn0YyOOdEUhFegl+ooonrsOP0CkYnUXemRBRcmmy3kTiwVw9GalnPIh ypJYEph7egjpw== Message-ID: <296662bf-66b9-4343-9104-afc56309b7fb@kernel.org> Date: Tue, 7 Jul 2026 15:51:49 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v3] mm: retry page faults under per-VMA lock when mmap_lock is not required To: Hongru Zhang , akpm@linux-foundation.org, linux-mm@kvack.org Cc: ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, baohua@kernel.org, shakeel.butt@linux.dev, linux-kernel@vger.kernel.org, Hongru Zhang References: <20260626075019.1833065-1-zhanghongru@xiaomi.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: bfruy9fdb613txetjqyydwi3rbonum96 X-Rspamd-Queue-Id: 84C298000F X-Rspamd-Server: rspam01 X-Rspam-User: X-HE-Tag: 1783432314-9872 X-HE-Meta: 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 18YXT2UJ QuAio/xElwkm6+BCGWoDeo7rKvb6RBOwZRJOtQzBgEgmwaxaV6L+0gBc8i1VgjPc3ChTQGmgA0MKGsbh2UaOACYuFWI7yhqO4bOogsEnmNLURh02oh6Aq+0oWl3ZFneCdlJkXGhhxFfKeBrGTYXNh95xJuxFcpBWwcx89BSeMaHlzblSNTxOIvHNjP6xi2ENcRxEntAtu+pX4jqSGbhjFfkFuDW09gd6zhaeMXNcZyJGyMD8Y9+C5cWuuAO0d0UAppWofLhkvrTalO7Sqowo/2VfluGjTbzS6c03cYLv58+A/juJRWoKlLUv8O2KIhBveV8yddjwX6wrXLgg= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/26/26 09:50, Hongru Zhang wrote: > From: Hongru Zhang > > Currently, when a page fault returns VM_FAULT_RETRY under the per-VMA > lock due to folio_lock() failing, mainly because the folio is under > I/O, the architecture fault handler unconditionally falls back to > retrying with mmap_lock. This leads to mmap_lock contention. > > This patch introduces VM_FAULT_RETRY_HARD to mark the paths that > require mmap_lock. Really sorry, but what a bad name :) Can we just embed the "no VMA lock" or "MMAP_LOCK" in the name somehow? VM_FAULT_RETRY_NEED_MMAP_LOCK VM_FAULT_RETRY_NO_VMA_LOCK Something like that? Also, we should document what the new flag means, and how it, for example, is always accompanied by VM_FAULT_RETRY. Best to be as clear as possible on the intended semantics. -- Cheers, David