Date: Thu, 6 Aug 1998 23:40:00 -0700 (PDT) From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: freebsd-bugs@FreeBSD.ORG Subject: Re: kern/7415 Message-ID: <199808070640.XAA18117@freefall.freebsd.org>
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The following reply was made to PR kern/7415; it has been noted by GNATS. From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: freebsd-gnats-submit@freebsd.org Cc: Subject: Re: kern/7415 Date: Fri, 07 Aug 1998 08:27:24 +0200 ------- Forwarded Message From: Luoqi Chen <luoqi@chen.ml.org> Message-Id: <199807281445.KAA19921@chen.ml.org> To: bde@zeta.org.au, freebsd-bugs@FreeBSD.ORG, luoqi@chen.ml.org, phk@FreeBSD.ORG Subject: Re: kern/7415 In-Reply-To: <199807281056.UAA30494@godzilla.zeta.org.au> X-UIDL: 0bb3b238bf5e8a0a5e0814b07eec4131 > >it sounds to me like the simple solution would be to either: > >A) have ufs clear the vmio flag agan > >B) have msdosfs (and other similar fs) clear the flag before they start. > > Simple and wrong. File systems know nothing of the vmio flag. Either > vm should clear it and be more careful about setting it (it only works > now for ufs because ufs never requests a misaligned block), or it should > always be set for block devices and fixes like the ones in the patch > should be applied. > > >Could you explain what your patch does ? > > It attempts to make misaligned buffers (ones whose size and file offsets > are multiples of PAGE_SIZE) actually work. It isn't clear whether they ^ not > were intended to work, but they will need to work if the buffer cache > and vm are ever fully merged. > > Bruce > Bruce explained it very well (much better than I could). I'd like make one comment, I believe the misaligned buffers are intended to work. The evidence is at around line 1830 of vfs_bio.c the statement, ((vm_offset_t) bp->b_data) |= off & PAGE_MASK; and in numerous other places statements like pmap_qenter(trunc_page(bp->b_data), bp->b_pages, bp->b_npages); the original author were aware of these misaligned buffers and attempted to make them work. - -lq ------- End of Forwarded Message To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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