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From: Shakeel Butt To: Michal Hocko Cc: alexei.starovoitov@gmail.com, bpf@vger.kernel.org, andrii@kernel.org, memxor@gmail.com, akpm@linux-foundation.org, peterz@infradead.org, vbabka@suse.cz, bigeasy@linutronix.de, rostedt@goodmis.org, houtao1@huawei.com, hannes@cmpxchg.org, willy@infradead.org, tglx@linutronix.de, jannh@google.com, tj@kernel.org, linux-mm@kvack.org, kernel-team@fb.com Subject: Re: [PATCH bpf-next v3 1/6] mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation Message-ID: References: <20241218030720.1602449-1-alexei.starovoitov@gmail.com> <20241218030720.1602449-2-alexei.starovoitov@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 1879140002 X-Rspam-User: X-Stat-Signature: 5spdsurdtrpx8tmrychyhkaaara9qhw6 X-HE-Tag: 1734566698-3204 X-HE-Meta: U2FsdGVkX18XCgAwd3f9fQve+k6cx/FmDzwVNiVG1QY5+boCK8ygRr05ZSj4t/gzoe4F3d5QwRaXJ2know07Rdc7ZkVdRgXLWeWvOrwo3ILeFLN5FDxUUiObEb32Ly3yB7G2wVHsvor/qzJgPWxAJmT9GT87cZU9c9aKnwugYEB2NL1ZvXvnQk7p3ylXZMAPBJaypzIrAobDfHeCLB1Bc1cPI9HDIhbl4GD/G/9xFYPAVojm5dnzZpel/c0M7qBXgf1I8RjO3rhGlxUqCPvCkZcXpstasjesO/ET5J8qKmR1chLE63IemldbxK4ylmZp64z306RtybyUO8jq/z5JuLVNQcmZ718ghNmlwOhlt029lBXIBCO+Y5AaWLiFj6tV9YvSagkUmG0GSiLEONFEusab1IJZoMdmX5fyOBDLMcoR6ULX8Cr3rmjXwA72+exE/qtIrA72ceirBJCADVjO+HEG5zS0mpszcfAZB9Beb/jImU1CdmP9HmwyZQUGBnYOA91Vfn/wR3/6HhpFN2OGT+PqVGRKgu+ol+sstncFTFFDDMkRUloS03lMuFdd2nKRWc/dzUcUaru3dJ8tT12UAcQLnHn9mfYjJt+soxh+zcqaOGnnDAfdgVh//al05C838BVukLKkxplo/cWQKq/QiqptgJw4F4Yk9Qsmo0wexM9+ZCHT2r+NbSubbLqGIVQUB9xRGh6g6h4ViPIuYRz4RKWsM4NnFph70izDTDdO6LnFAr5SALZyKNpu5SQ1/OTCJlsOFY95flh15gAJAzTqHWBY8iqEEafNIGDYqWOkefv6fO9VNMTIUudPkhG2uNLrPzSTr63hXNiLXQPik0v8rk+rgN3aTqNpAHtWeeK8KiXjZOqtVHVKOII7Ns0fnyro3IboTm1onmnaD90ONlYRg5eI8WLXiXMvtOlt8aOXKvQvOKDTrsT8ANrXpVRk0R/WNs/EQK/x/nnPclViMTu IvnMUMx7 n1XaMbM9Mg0cO2RTm0tzp2+G0+Y1Ojqh5pyt6t+NAn2zdRHwM9FJ6/ffJQ/+pJb32gXhTbEV7i+HlLRq5RMNtqReA8ay1qqxhZv9CaYMit57h/iAjWFKmzcXDcrKeEgoNUhjNVa9kEIisY8pLKbU2V3/HI+JzmtxgbE+31lN6GwKyhWLOHxAIqUhidf0vbnas27LwDAOpAQ+4daXEhCHxMlS5FWpyop3IZhf9ILoeuk21pnVufinR1IYJNeyDokwyk0YjNczqQdy8t4lntAzGVMUSyHtiOTHMTG8o 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 Wed, Dec 18, 2024 at 12:32:20PM +0100, Michal Hocko wrote: > I like this proposal better. I am still not convinced that we really > need internal __GFP_TRYLOCK though. > > If we reduce try_alloc_pages to the gfp usage we are at the following > > On Tue 17-12-24 19:07:14, alexei.starovoitov@gmail.com wrote: > [...] > > +struct page *try_alloc_pages_noprof(int nid, unsigned int order) > > +{ > > + gfp_t alloc_gfp = __GFP_NOWARN | __GFP_ZERO | > > + __GFP_NOMEMALLOC | __GFP_TRYLOCK; > > + unsigned int alloc_flags = ALLOC_TRYLOCK; > [...] > > + prepare_alloc_pages(alloc_gfp, order, nid, NULL, &ac, > > + &alloc_gfp, &alloc_flags); > [...] > > + page = get_page_from_freelist(alloc_gfp, order, alloc_flags, &ac); > > + > > + /* Unlike regular alloc_pages() there is no __alloc_pages_slowpath(). */ > > + > > + trace_mm_page_alloc(page, order, alloc_gfp & ~__GFP_TRYLOCK, ac.migratetype); > > + kmsan_alloc_page(page, order, alloc_gfp); > [...] > > From those that care about __GFP_TRYLOCK only kmsan_alloc_page doesn't > have alloc_flags. Those could make the locking decision based on > ALLOC_TRYLOCK. > > I am not familiar with kmsan internals and my main question is whether > this specific usecase really needs a dedicated reentrant > kmsan_alloc_page rather than rely on gfp flag to be sufficient. > Currently kmsan_in_runtime bails out early in some contexts. The > associated comment about hooks is not completely clear to me though. > Memory allocation down the road is one of those but it is not really > clear to me whether this is the only one. Is the suggestion that just introduce and use ALLOC_TRYLOCK without the need of __GFP_TRYLOCK? Regarding KMSAN, the __GFP_ZERO would bypass it. Maybe a comment to explain that.