Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!umd5!brl-adm!adm!rbj@icst-cmr.arpa From: rbj@icst-cmr.arpa (Root Boy Jim) Newsgroups: comp.unix.wizards Subject: Delayed writes on removed files Message-ID: <13188@brl-adm.ARPA> Date: 29 Apr 88 16:24:01 GMT Sender: news@brl-adm.ARPA Lines: 42 From: Amos Shapir Here is something new for a change: When a file is removed, its blocks are released to the free list. If any writes were done, some of these blocks may still be in the buffer pool, waiting for a delayed write. When such buffers are reallocated, they will be written to the disk, even though their contents are no longer relevant. I find this hard to believe. If there *are* blocks waiting to be read, they must be associated with an inode, which is in core, and is therefore open by someone. If the file is removed, the link count in core will still be (at least) one, and I/O should happen normally, even tho the file has no directory entrys. The systems I have checked - 4.2 and sysV.3 - make no effort to prevent this. It seems that in an environment in which many files are created, written to, and then discarded (e.g. compilation) preventing unnecessary writes to disk may have a significant effect on overall system performance. Does anyone know of a system that does this, and how? When the file *is* finally closed, the inode ref count becomes zero, and the system should just ignore the delayed write flag and move the blocks to the free list. Seems simple enuf, but I have not read the code to check if it in fact does this. Perhaps it isn't even necessary, as blocks are only allocated on writes, which then overwrite the old data. I can't imagine that the old sata would be written first, but truth is stranger than fiction. Chris, say it ain't so! Amos Shapir (My other cpu is a NS32532) National Semiconductor (Israel) 6 Maskit st. P.O.B. 3007, Herzlia 46104, Israel Tel. +972 52 522261 amos%taux01@nsc.com 34 48 E / 32 10 N (Root Boy) Jim Cottrell National Bureau of Standards Flamer's Hotline: (301) 975-5688 The opinions expressed are solely my own and do not reflect NBS policy or agreement .. If I had heart failure right now, I couldn't be a more fortunate man!!