On Fri, Dec 15, 2000 at 05:57:18PM +0000, Alan Cox wrote:
> How hard is it to seperate losing kpiod (optimisation) from the MAP_SHARED
> changes ? I am assuming they are two seperate issues, possibly wrongly
Losing kpiod isn't an optimization ;(. Losing kpiod is the MAP_SHARED bugfix.
The problem was:
o swap_out
o wants to flush a MAP_SHARED dirty page to disk
o so allocate kpiod-struct
o sumbit the page-flush request to kpiod
o don't wait I/O completion to avoid deadlocking on the i_sem
o swap_out returns 1 and memory balancing code so thinks we did progress
in freeing memory and goes to allocate memory from the freelist
without waiting I/O completion
o repeat N times the above
o in the meantime kpiod has a big queue but it's blocked slowly writing
those pages to disk
o while it writes a few pages swap_out floods again the queue
without waiting and it empties the freelist (task killed)
The problem was the lack of write throttling due the kpiod async-only nature.
> Providing no inode semaphore is upped from a different task , which seems
> currently quite a valid legal thing to do (ditto doing the up on completion of
> something in bh or irq context)
Yes, the same `current' context must run the down/up pair of calls and as you
said it is legal to rely on it on all the places it's used.
Andrea
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