Date: Fri, 23 Jan 2004 12:50:25 -0800 (PST) From: Radim Kolar <hsn@netmag.cz> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/61691: very bad performance of realloc()/brk() Message-ID: <200401232050.i0NKoP7P059551@freefall.freebsd.org>
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The following reply was made to PR kern/61691; it has been noted by GNATS. From: Radim Kolar <hsn@netmag.cz> To: Poul-Henning Kamp <phk@FreeBSD.org> Cc: freebsd-bugs@FreeBSD.org, bug-followup@freebsd.org Subject: Re: kern/61691: very bad performance of realloc()/brk() Date: Fri, 23 Jan 2004 16:20:35 +0100 > You seem to be confused as to what responsibilities the programmer > has when it comes to practicing sensible memory management. I have run some benchmarks for you. There are doing 32 times realloc() in 1 MB chunks. I don't think that this is example of bad programming practice. The major problem is that realloc() copies data while Linux doesn't. FreeBSD 5.2 =========== It looks that brk() syscall is quite slow in FreeBSD when comparing against Linux. FreeBSD calls 32 times brk() and 10 times mmap+munmap (for page directory). (hsn@ttyv0):~/forkbomb% time ./forkbomb -l 32 -i 256 -M --quit 12:45 Safety alarm at 300 sec. enabled. Actions: alloc 32 MB (step 1024 kB) and touch it. Forkbomb 1.2 started. ./forkbomb -l 32 -i 256 -M --quit 4.58s user 5.28s system 74% cpu 13.159 total linux2.4+glibc2.3.2 =================== Linux does 1 times mmap + 31 times mremap syscall Safety alarm at 300 sec. enabled. Actions: alloc 32 MB (step 1024 kB) and touch it. Forkbomb 1.2 started. ./forkbomb -l 32 -i 256 -M --quit 0.00s user 0.30s system 107% cpu 0.280 total Well my pr-report/wish is: optimize realloc() function (which is about 3 pages long) to avoid copying data while brk() is sufficient , because the reallocated block is last block.
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