2017-09-27 7:59 GMT+08:00 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>: > On Fri, 22 Sep 2017 07:12:32 +0800 Yafang Shao <laoar.shao@xxxxxxxxx> wrote: > >> we can find the logic in domain_dirty_limits() that >> when dirty bg_thresh is bigger than dirty thresh, >> bg_thresh will be set as thresh * 1 / 2. >> if (bg_thresh >= thresh) >> bg_thresh = thresh / 2; >> >> But actually we can set vm background dirtiness bigger than >> vm dirtiness successfully. This behavior may mislead us. >> We'd better do this validity check at the beginning. >> >> ... >> >> --- a/Documentation/sysctl/vm.txt >> +++ b/Documentation/sysctl/vm.txt >> @@ -156,6 +156,9 @@ read. >> Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any >> value lower than this limit will be ignored and the old configuration will be >> retained. >> +Note: the value of dirty_bytes also cannot be set lower than >> +dirty_background_bytes or the amount of memory corresponding to >> +dirty_background_ratio. > > I think this means that a script which alters both dirty_bytes and > dirty_background_bytes must alter dirty_background_bytes first if they > are being decreased and must alter dirty_bytes first if they are being > increased. Or something like that. > Yes. > And existing scripts which do not do this will cease to work correctly, > no? > The existing scritpts won't work correctly. That's also what I have worried before. But under this condition, there's a error message generated by "sysctl -w" to tell them the first setting was failure. This error message may be a reminder to them that there are some connections between background and direct limit, and should not set arbitrary. May that's better. I'm not sure. Thanks Yafang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
