Date: Thu, 14 Aug 2003 15:30:56 -0700 From: David Schultz <das@FreeBSD.ORG> To: Eno Thereska <eno@andrew.cmu.edu> Cc: freebsd hackers <freebsd-hackers@FreeBSD.ORG> Subject: Re: increasing number of buffers in BSD4.4 Message-ID: <20030814223056.GA67495@HAL9000.homeunix.com> In-Reply-To: <3F3BD31A.8080808@andrew.cmu.edu> References: <3F3BD31A.8080808@andrew.cmu.edu>
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On Thu, Aug 14, 2003, Eno Thereska wrote: > In McKusick's book "The design and Implementation of the 4.4BSD > Operating system", in the "Buffer Management subsection > of the I/O system overview, there is a a sentence that says > "...depending on available memory, a system is configured with from > 100 to 1000 buffers.." referring to the number of struct buf* in the > integrated VM/IO buffer cache. > > I have plenty of RAM in my computer, but it seems like there are always > 1000 buffers configured (empirical observation, if I try to allocate > one more after that the system freezes). How do I increase the nubmer of > buffers? More consicely, how do I allocate more memory to the buffer > management subsystem? In FreeBSD, you get 1 buffer for every megabyte of memory up to 64 MB of RAM, and 1 buffer for every 2.5 megabytes after that. See kern_vfs_bio_buffer_alloc() in vfs_bio.c. On i386 and amd64, there's a cap of about 1000 due to KVA limits, although that cap should not be needed for amd64.
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