On 7/3/18 10:05 AM, Yang Shi wrote:
On 7/3/18 3:39 AM, Theodore Y. Ts'o wrote:
On Tue, Jul 03, 2018 at 12:11:18PM +0800, Yang Shi wrote:
direct reclaim doesn't write out filesystem page, only kswapd could do
it. So, if the call comes from direct reclaim, it is definitely a bug.
And, Mel Gormane also mentioned "Ultimately, this will be a BUG_ON." In
commit 94054fa3fca1fd78db02cb3d68d5627120f0a1d4 ("xfs: warn if direct
reclaim tries to writeback pages").
Although it is for xfs, ext4 has the similar behavior, so elevate
WARN_ON to BUG_ON.
And, correct the comment accordingly.
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
What's the upside of crashing the kernel if the file sytsem can
handle it?
BTW, the comment does sound misleading. Direct reclaim is not a
legitimate context to call writepage. I'd like to correct at least.
Thanks,
Yang
I'm not sure if it is a good choice to let filesystem handle such
vital VM regression. IMHO, writing out filesystem page from direct
reclaim context is a vital VM bug. It means something is definitely
wrong in VM. It should never happen.
It sounds ok to have filesystem throw out warning and handle it, but
I'm not sure if someone will just ignore the warning, but it should
*never* be ignored.
Yang
- Ted
