Date: Tue, 24 Sep 1996 17:21:26 +0200 From: Poul-Henning Kamp <phk@critter.tfs.com> To: Luigi Rizzo <luigi@labinfo.iet.unipi.it> Cc: hackers@FreeBSD.ORG, bde@FreeBSD.ORG, asami@FreeBSD.ORG Subject: Re: Optimizing bzero() Message-ID: <304.843578486@critter.tfs.com> In-Reply-To: Your message of "Tue, 24 Sep 1996 09:38:24 %2B0200." <199609240738.JAA00165@labinfo.iet.unipi.it>
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Luigi, The problem really is that you need a couple of parameters more to malloc: void * my_wish_malloc( int bytes, int flags, int *length) bytes is the number of bytes you want. flags can be used to specify various options: ZERO -- please clean it for me. EXTEND -- I may ask you for more later in *length malloc will tell you how much you actually got ie you malloc(129) and it will tell you 256 bytes are there for you. Next you need a indirect version: void * my_wish_imalloc( int bytes void **ptr, int flags int *length); Same as above, except that the only pointer the program uses to access the memory is *ptr, thus malloc can realloc the memory without telling the process merely by updating *ptr to point to the new place. Now you can start to optimize things, but as long as we cannot talk more efficiently with malloc, it's not really much use to change the behaviour. If we had this kind of interface, it would be a sensible thing for malloc to do to send pages to the kernel-idle-washer for cleaning, but with the interface has been cast in iron by POSIX: forget it. The next thing you could start to consider is when people realloc a multipage allocation to something bigger, it would be nice to be able to ask the kernel to "move these pages to this address" and then extend It there instead of copying the contents. and so on... Fortunately, I can promise you that we are squarely up against the wall of diminishing return here: Just the madvise case happens a lot less than you would think. (Do you have access to a PostScript printer with a good resolution ? A4@600dpi or better ? I can send you some files that will show you what I mean). BTW: I have still not decided if the madvise should use _FREE or _DONTNEED yet, it must depend on experience. Finally, if you really want to get something done, make stdio use mmap instead of read on regular files... You save a page per FILE * you open and a bcopy of the contents of the file... I know writes are tricky, so just do it for read-only FILE *'s initially. -- Poul-Henning Kamp | phk@FreeBSD.ORG FreeBSD Core-team. http://www.freebsd.org/~phk | phk@login.dknet.dk Private mailbox. whois: [PHK] | phk@ref.tfs.com TRW Financial Systems, Inc. Future will arrive by its own means, progress not so.
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