Hi folks, would the Linux implementation grock multiple finfo's about one file even with overlapping blocks ? say a finfo of ino 12345, followed by some finfo's of say ino 123400, followed by some more of ino 12345? Or does it implicitly assume a kind of ordering in the blocks? In *BSD, and especally in NetBSD, buffer cache and memory mapping is done FS agnostic by UVM/UBC. If a piece of file-mapped memory is deemed not needed anymore its pushed out as buffer, basicly a memory extent and its file/disc information. The pages describing that buffer are thus NOT at the FSs control and will only be released after it gets signalled its written out. I hope to save duplicating the written out data in memory by putting it directly into the to-be-written-out segment, this *might* result in pre-pending and moving data around if earlier blocks are written out later but can also mean that other file write pieces are interleaved. The block number assigning and its inode update and recording in the DAT i'll cache for sure since thats nearly no data. The reason for the mumbo jumbo is to avoid multiple storage of data: its in the buffer cache until its given the signal its written out. Normally this is just passed to the device and that shedules it and we're done and can/will be automagically released later. Since we want to create a log however and like to write out synchronous it has be copied and the buffer released ASAP to avoid possible long delays. If i would just write out all the blocks after a (yet) unfilled/unwritten partial segment header it would solve it but would also create heaps of disc write transactions and a retrace of the head on physical disks or a re-flash/relocation on SSD for the missing partial segment header. Performance would suffer a lot. Having best of both worlds would mean keeping two empty partial segment spaces around easily eating a few (possibly scarse) megabytes. One for construction, one for storage/overflow. You don't want to lose 4Mb for each mounted FS or is that not an issue you think? In short: what do you folks recommend? I like the two partial segment spaces and having a backup-way by direct writing for memory challenged machines, but would the linux way be and what would be a sane way? With regards, Reinoud Zandijk
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