Re: [PATCH] Provide an interface to limit total page cache.

["Roy Huang" <royhuang9@gmail.com>]

The possible cause is a bug in kswapd thread, or shrink_all_memory
cannot be called in kswapd thread.

On 1/15/07, Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> wrote:
> Roy Huang wrote:
> > A patch provide a interface to limit total page cache in
> > /proc/sys/vm/pagecache_ratio. The default value is 90 percent. Any
> > feedback is appreciated.
>
> [snip]
>
> I tried to run your patch on PPC64 SMP machine, unfortunately kswapd
> crashes the kernel when the pagecache limit is exceeded!
>
> ->dd if=/dev/zero of=/tmp/foo bs=1M count=1200
> cpu 0x0: Vector: 300 (Data Access) at [c0000000012d7ad0]
>     pc: c0000000000976ac: .kswapd+0x3a4/0x4f0
>     lr: c0000000000976ac: .kswapd+0x3a4/0x4f0
>     sp: c0000000012d7d50
>    msr: 8000000000009032
>    dar: 0
>  dsisr: 42000000
>   current = 0xc00000000fed7040
>   paca    = 0xc00000000063fb80
>     pid   = 134, comm = kswapd0
> ------------[ cut here ]------------
> enter ? for help
> [c0000000012d7ee0] c000000000069150 .kthread+0x124/0x174
> [c0000000012d7f90] c0000000000247b4 .kernel_thread+0x4c/0x68
> 0:mon>
>
> Steps to recreate fail:
>
> # sync
> # echo 1 > /proc/sys/vm/drop_caches
> MemTotal:      1014584 kB
> MemFree:        905536 kB
> Buffers:          3232 kB
> Cached:          57628 kB
> SwapCached:          0 kB
> Active:          47664 kB
> Inactive:        33160 kB
> SwapTotal:     1526164 kB
> SwapFree:      1526164 kB
> Dirty:             108 kB
> Writeback:           0 kB
> AnonPages:       19976 kB
> Mapped:          15084 kB
> Slab:            19724 kB
> SReclaimable:     8536 kB
> SUnreclaim:      11188 kB
> PageTables:        972 kB
> NFS_Unstable:        0 kB
> Bounce:              0 kB
> CommitLimit:   2033456 kB
> Committed_AS:    87884 kB
> VmallocTotal: 8589934592 kB
> VmallocUsed:      2440 kB
> VmallocChunk: 8589932152 kB
> HugePages_Total:     0
> HugePages_Free:      0
> HugePages_Rsvd:      0
> Hugepagesize:    16384 kB
>
> # echo 50 > /proc/sys/vm/pagecache_ratio
> # dd if=/dev/zero of=/tmp/foo bs=1M count=1200
>
> Basically fill pagecache with overlimit dirty file pages and check
> if the reclaim happened and the limit was not exceeded.
>
> --Vaidy
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