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AJvYcCWN61QmmPFaShnvipIry/7nW/Y30J13+pX9NPLqDW/+N3njiGFIc1oocXnO+3M/W+oXg24imJF0HQ==@kvack.org X-Gm-Message-State: AOJu0YzNoA5djjNtFJ4xwIK1VxI6jJxCnu2T5jsRr5olrUr3m8Q18xzP KSDekvWVGVyU4i86YN/fnrQnJCjMe3qwowM3A5u9Ng833PpKjLq4Xo3ejMGjzao2xqFFcKXJDwc AP/DeRe+3Gk81CMmke0V3r+6coso= X-Gm-Gg: ASbGncsZHUhdd5arqsIGuc3ogSk2KdL+LLzNVZV16KYf9lLQq6hENnMJDLbhVL0FE+l f3Z4TbkGGjsipsitSB7G60oXeXGUQ4iMAX1wmgTlrjYohRLQq7GQ= X-Google-Smtp-Source: AGHT+IHRXMV1lFc2pyP86vUXtoVTDycn1vVBECYM/6TXKG1ySVASPzUJp/8TO1FjhGw5v5tOUav1fgaVwGILxAU6izY= X-Received: by 2002:a05:6000:156f:b0:385:efc7:9348 with SMTP id ffacd0b85a97d-3864ce86411mr451921f8f.1.1733866936462; Tue, 10 Dec 2024 13:42:16 -0800 (PST) MIME-Version: 1.0 References: <20241210023936.46871-1-alexei.starovoitov@gmail.com> <20241210023936.46871-2-alexei.starovoitov@gmail.com> In-Reply-To: From: Alexei Starovoitov Date: Tue, 10 Dec 2024 13:42:05 -0800 Message-ID: Subject: Re: [PATCH bpf-next v2 1/6] mm, bpf: Introduce __GFP_TRYLOCK for opportunistic page allocation To: Matthew Wilcox Cc: bpf , Andrii Nakryiko , Kumar Kartikeya Dwivedi , Andrew Morton , Peter Zijlstra , Vlastimil Babka , Sebastian Sewior , Steven Rostedt , Hou Tao , Johannes Weiner , shakeel.butt@linux.dev, Michal Hocko , Thomas Gleixner , Tejun Heo , linux-mm , Kernel Team Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 98figamiegzefaicp5aztq1a5njmaim3 X-Rspamd-Queue-Id: 78782C001B X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1733866928-771502 X-HE-Meta: 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 OzNjUjYU aFxjBXhCxsUg8GOisUK7mE88Cue+GMNqwsh9HO7eWgYcEqdrJoYZ4wj+uGCJXu1jersFl1m1IAjOlppB9nnbBuQjmmCAjKWmWJmcOvVAjYlmGNQ+6GaaKtd2itjncvcJHM29dVX2EAgfx6H/bS0ucjHgAjuhV0qQvHxS5JReHdPHM+78gbWh2m9keROVkzDmAg7oHz6HcDM/H+KcSkFvfRLdzo9yk2QvRaTfTAJfMPjp1xrOHSenCVZrBNEbiHCgg2xGp/D9b7Rf1ka6fXIJAzyCnZK0wsx/ynYHM2EG9xc/E0uuVFeb82m8JO+rg7goGjca7FSUDiEuzp/teyafzNU8W7VOhBHnh0R6OUP7XxCUTdkkgyhNqVfyJo+QbOskgku1WubM30GGQpFGbO7rvYyV8p0Ps7XNqtXSliZ3rtpeJGFlrfVc9fF0Jk6O999+ZKyVrGHAI8/H1GGU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.035473, 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, Dec 9, 2024 at 9:31=E2=80=AFPM Matthew Wilcox = wrote: > > On Mon, Dec 09, 2024 at 06:39:31PM -0800, Alexei Starovoitov wrote: > > + if (preemptible() && !rcu_preempt_depth()) > > + return alloc_pages_node_noprof(nid, > > + GFP_NOWAIT | __GFP_ZERO, > > + order); > > + return alloc_pages_node_noprof(nid, > > + __GFP_TRYLOCK | __GFP_NOWARN | __G= FP_ZERO, > > + order); > > [...] > > > @@ -4009,7 +4018,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask, unsigned int o= rder) > > * set both ALLOC_NON_BLOCK and ALLOC_MIN_RESERVE(__GFP_HIGH). > > */ > > alloc_flags |=3D (__force int) > > - (gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM)); > > + (gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM | __GFP_TR= YLOCK)); > > It's not quite clear to me that we need __GFP_TRYLOCK to implement this. > I was originally wondering if this wasn't a memalloc_nolock_save() / > memalloc_nolock_restore() situation (akin to memalloc_nofs_save/restore), Interesting idea. It could be useful to pass extra flags into free_page path, since it doesn't have flags today and I'm adding free_pages_nolock() in patch 2 just to pass fpi_t fpi_flags around. memalloc_nofs_save()-like makes the most sense when there are multiple allocations and code path attempts to be generic. For bpf use case it's probably overkill. I guess we might have both __GFP_TRYLOCK and memalloc_nolock_save() that clear many flags. Note it needs to clear __GFP_KSWAPD_RECLAIM which is not safe when raw spin lock is held. > but I wonder if we can simply do: > > if (!preemptible() || rcu_preempt_depth()) > alloc_flags |=3D ALLOC_TRYLOCK; I don't think we can do that. It will penalize existing GFP_ATOMIC/NOWAIT users. kmalloc from RCU CS with GFP_NOWAIT is fine today.