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[90.235.19.70]) by smtp.gmail.com with ESMTPSA id h13-20020ac2596d000000b004f37ae2e718sm1644981lfp.3.2023.05.24.02.20.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 May 2023 02:20:41 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 24 May 2023 11:20:39 +0200 To: Thomas Gleixner Cc: Christoph Hellwig , linux-mm@kvack.org, Andrew Morton , Uladzislau Rezki , Lorenzo Stoakes , Peter Zijlstra , Baoquan He Subject: Re: [patch 4/6] mm/vmalloc: Check free space in vmap_block lockless Message-ID: References: <20230523135902.517032811@linutronix.de> <20230523140002.747157575@linutronix.de> <20230523152939.GD12341@lst.de> <87edn7uimx.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87edn7uimx.ffs@tglx> X-Rspamd-Queue-Id: E1F0C40016 X-Rspam-User: X-Stat-Signature: rg1hmss46wjskrzesichr78rajj8a6so X-Rspamd-Server: rspam01 X-HE-Tag: 1684920043-521409 X-HE-Meta: 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 2lLaevq1 /Tq7+hcvY+Pvxrf3SBfLEmmsvmDE+VyMQ5wiV/NXUAwbXsF0EBoUODiU9sKpPeqKzoyCR/eeQ3zrsZv32ZXWDSAEnCFpD0XrlJKxjitsmIlXLXm/EKjYyZkhDn5MZ/uX8jKATH0sNVwiYaXaSx9uAmrUWdb6OJOLsmiYurvcXxgivwazR/y0gt7aMdSILMFIzDeQ8ewux4tU71POEgLzRtIO+zEBI9R6hMHkveXc8oBV07giwDxI9oK/u6IMg/EocDF7mNamblSZX/ovROa/BfsxSWH5oRsPsn8aBpfn3ivcYHwtnb383mRi6vFsHNIsTTYgjPaMb4B6vli1oPuWv+rPsEKcDChK/6mFbsBUof2IgyoL51Dw8QDFgkCnbpKwQy4aBehrqbPsp9l3MqJq4TlHIwoVPiujKZn8BRcj1E0GU/VAoIwJ8cSXyJ9gE7CSk+iFDU3RpL7UCXegd7af9pkozMg== 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 Tue, May 23, 2023 at 06:17:42PM +0200, Thomas Gleixner wrote: > On Tue, May 23 2023 at 17:29, Christoph Hellwig wrote: > > On Tue, May 23, 2023 at 04:02:14PM +0200, Thomas Gleixner wrote: > >> + if (READ_ONCE(vb->free) < (1UL << order)) > >> + continue; > >> + > >> spin_lock(&vb->lock); > >> if (vb->free < (1UL << order)) { > >> spin_unlock(&vb->lock); > >> @@ -2174,7 +2177,7 @@ static void *vb_alloc(unsigned long size > >> > >> pages_off = VMAP_BBMAP_BITS - vb->free; > >> vaddr = vmap_block_vaddr(vb->va->va_start, pages_off); > >> - vb->free -= 1UL << order; > >> + WRITE_ONCE(vb->free, vb->free - (1UL << order)); > > > > Maybe just a matter of preference, but wouldn't an atomic_t be > > better here? We'd have another locked instruction in the alloc > > path, but I always find the READ_ONCE/WRITE_ONCE usage a bit > > fragile that I'd rather reserve them to well documented hot > > path code. > > I don't see a problem with these lockless quickchecks, especially not > in this particular case, but no strong opinion either. > Reviewed-by: Uladzislau Rezki (Sony)