Hello, Kostik. You wrote 8 января 2011 г., 23:20:28: >> >> And, if it is "classic deadlock" is here any "classical" solution to >> >> it? >> > Do not allocate during bio processing. >> So, if GEOM need some cache, it needs pre-allocate it and implements >> custom allocator over allocated chunk? :( >> >> And what is "bio processing" in this context? geom_raid5 puts all > bio processing == whole time needed to finish pageout. Pageout is > often performed to clean the page to lower the page shortage. > If pageout requires more free pages to finish during the shortage, > then we get the deadlock. Ok, and transmission mmap() files on geom_raid5, so when these pages are paged out, and geom_raid5 asks for other pages, and there is no free ones... I see. It seems, that M_NOWAIT flag should help, if geom_raid5 could live with failed mallocs...
> Also, it seems that you allocate not only bios (small objects, not > every request cause page allocation), but also the huge buffers, that > require free pages each time. Yes, in worst case RAID5 need a lot of additional memory to perform simple write. If it is lone write (geom_raid5 waits some time for writes in adjacent areas, but not forever), geom_raid5 need to read (Number of disks - 1) x (size of write) bytes of data to re-calculate checksum. And it need buffers for this data. Worst case for 5-disks RAID5 and 128KiB write will be 4x128KiB = 512KiB of buffers. For one 128KiB write. And I don;t understand how to avoid deadlock here :( Maybe, preallocating some memory at start (these 512KiB) and try to use them when malloc() failed... I need to look how raid3 and vinum/raid5 lives with that situation. -- // Black Lion AKA Lev Serebryakov <l...@freebsd.org> _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
