On 07/23/20 at 11:21am, Mike Kravetz wrote: > On 7/23/20 2:11 AM, Baoquan He wrote: > > On 07/23/20 at 11:46am, Anshuman Khandual wrote: > >> > >> > >> On 07/23/2020 08:52 AM, Baoquan He wrote: > >>> A customer complained that no message is logged wh en the number of > >>> persistent huge pages is not changed to the exact value written to > >>> the sysfs or proc nr_hugepages file. > >>> > >>> In the current code, a best effort is made to satisfy requests made > >>> via the nr_hugepages file. However, requests may be only partially > >>> satisfied. > >>> > >>> Log a message if the code was unsuccessful in fully satisfying a > >>> request. This includes both increasing and decreasing the number > >>> of persistent huge pages. > >> > >> But is kernel expected to warn for all such situations where the user > >> requested resources could not be allocated completely ? Otherwise, it > >> does not make sense to add an warning for just one such situation. > > > > It's not for just one such situation, we have already had one to warn > > out in mm/hugetlb.c, please check hugetlb_hstate_alloc_pages(). > > Those are a little different in that they are warnings based on kernel > command line parameters. > > > As Mike said, in one time of persistent huge page number setting, > > comparing the old value with the new vlaue is good enough for customer > > to get the information. However, if customer want to detect and analyze > > previous setting failure, logging message will be helpful. So I think > > logging the failure or partial success makes sense. > > I can understand the argument against adding a new warning for this. > You could even argue that this condition has existed since the time > hugetlb was added to the kernel which was long ago. And, nobody has > complained enough to add a warning. I have even heard of a sysadmin > practice of asking for a ridiculously large amount of hugetlb pages > just so that the kernel will allocate as many as possible. They do > not 'expect' to get the ridiculous amount they asked for. In such > cases, this will be a new warning in their log. > > As mentioned in a previous e-mail, when one sets nr_hugepages by writing > to the sysfs or proc file, one needs to read the file to determine if the > number of requested pages were actually allocated. Anyone who does not > do this is just asking for trouble. Yet, I imagine that it may happen. > > To be honest, I do not see this log message as something that would be > helpful to end users. Rather, I could see this as being useful to support > people. Support always asks for system logs and this could point out a > possible issue with hugetlb usage. > > I do not feel strongly one way or another about adding the warning. Since > it is fairly trivial and could help diagnose issues I am in favor of adding > it. If people feel strongly that it should not be added, I am open to > those arguments. Seems it's all done, and very fair. I appreciate your understanding on this issue. Will see if any strong concern is raised on the log adding.
