Messages in this thread | | | From | "Anthony Barbachan" <> | Subject | Interesting apparent increased instability and eventual death after memory/CPU upgrade on a 2.0.36 heavily used server | Date | Wed, 17 Mar 1999 02:22:08 -0500 |
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This is an interesting situation perhaps related to a kernel bug in 2.0.36? After giving a heavily used server a CPU and memory upgrade I have been getting "Running low on DMA buffers" warning at times when accessing a SCSI CDROM (also at least once during the access of a SCSI tape) on a Adaptec 1542B. The only other SCSI device on the chain is a hard drive which receives moderate to heavy useage by samba and NFS. Several other non-SCSI devices are also present but do not exibit any unusual behavior. (modems, both internal and external, a Digiboard X/EVE 2 port serial board, EIDE hard drive, 3c509B network card, printer) Before the memory and CPU upgrade this server was functioning very well despite its limited resources. The upgrade consisted of a doubling of the memory to 32MB (from 16MB) and the swaping of the Pentium 75 processor to a Pentium 90. Both parts should be perfectly fine as they were previously present and functioning correctly in other systems. In any case after several days of getting ocassional "Running low on DMA buffers when accessing the tape and/or CDROM drive today the machine died when mounting a CDROM (perhaps a very relevent fact, the SCSI hard drive was under heavy useage by Samba at the time). I got a bunch of running low on DMA buffers, just like before, then several messages stating that the Adaptec was swithing to regular I/O. Finally I got a kernel panic, "trying to free page," and the system froze completely dead, not even an Ooops. I have an idea more or less why this is happening; as the Adaptec SCSI card is ISA it can't do DMA over the first 16MB of memory and since before all the memory was below this barrier it was probably quite simple before for the kernel to free up some memory for a DMA buffer. However I have used a similar SCSI card on my personal system (an Adapter 1542CF) which has 128MB with no problems (although it is much less used there). Is this a known 2.0.36 issue and is there a fix for it? Would an upgrade to 2.2.3 on the afflicted server aliviate the problem?
In case I need to modify the source to implement my own fix to this problem; this is what I currently have in mind. Allocate a pool of ISA DMA capable memory upon the Adapter driver's initialization, from which the driver will get buffers for DMA memory requests (Best case would be a pool big enougth to accomodate all possible concurrent SCSI DMA usuages; anyone have any idea how big that would have to be?). Suggestions, ideas, comments welcome.
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