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U2FsdGVkX1/dkzLqXeQOOwjz2PAMvalWI5f+7gDegOun5CrAq6BTOSIUQ/3RXDxXNRDmP20rw0Dzjia8Ht3wnZ74t6Zl1V6pFww+TJAqrM/j1VcCvHj3a/TV795PafqDYnTIMHof407fN2io3r9xo2Y3QmJOFLGTovSUZf73uidGKpWK/+wLRyaZGa/A+wZEaKV89us0sGJazhYuKajTOqb4xJy38I70zcejPxUIqce+bz7WpoGFSvr1h0LvQ4p5prypUJcSCjVSjoKWLv75bmB8L/IUtR73yJxRVqlDscMkoWKoGzD1hEBFyd7arInZFOrSNmTqq+YIrNZpbA4FCSnD8AK9yvpRcmbe4hrLWXCEllzsaurXyCEC3rlGIpxtJ8BpGMAqfAz+b2bPLkiRFBxO6Ntslq8YXosIIlDZalxIRgDABcGfG9gW1UjWxmp5/uwdqWUNWRKL9AIpuca3oUHkGY3V3WJrCYFcOMeFV2bixVVw072QcHLzcACK7Z4Uy6aeNHLRrSmP8Wt/FHKtKOWeGU04+sftp8Dqb5TSTPvuZ/FhQ5Yn3CV3RF7qqPu0MM8wk52LvTtXB1lTmM4CFKBPi7qK3sW2eyJjCVmw+sgaCBBgmbPbAeak/PQaVpbFwA35ztzd8FMhPSEb6zw0doBiPqjozR03e9N8+DxXYF6xdZT4KP6kZVHoemaWmqUa0nidtfWTiyvO4ifXthL1e0Ui7dgmryG5iiKpbS1rcURp9VeiB57PyIaUDg5bIPbKP28iM9BHiQjdGtUabbBJO31IGIoMrVAsC2at+uJF8UQC75zgwwn/QeIzuWJeAK0/08s6D/6BDzl7MUYZ/1HjVEPZvFWwTl2nmBzpUZH7pKSR+biFC09qVX69R7dtUKPgj8vcgCSrtTRnrdh5goR3cf5XdyAviAnwQcSszFlt2OTPRM4Sf77dU3rc6jppKh/uDtCaUifzG4Kw2i+DJOf PcsWhDE6 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 07/30/23 20:51, Xueshi Hu wrote: > When writing to /proc/sys/vm/nr_huge_pages, it indicates global number of > huge pages of the default hstate. But when reading from it, it indicates > the current number of "persistent" huge pages in the kernel's huge page > pool. > > There are currently four interfaces used to export the number of huge > pages: > - /proc/meminfo > - /proc/sys/vm/*hugepages* > - /sys/devices/system/node/node0/hugepages/hugepages-2048kB/* > - /sys/kernel/mm/hugepages/hugepages-2048kB/* > > But only the /proc/sys/vm/nr_huge_pages provides the 'persistent' > semantics when reading from it. This inconsistency is very subtle and can > be easily misunderstood. Thanks for looking into this. The hugetlb documentation (./admin-guide/mm/hugetlbpage.rst) mentions the term 'persistent hugetlb pages', but never provides a definition. We can get the definition from the code as: #define persistent_huge_pages(h) (h->nr_huge_pages - h->surplus_huge_pages) Further, the documentation says: "The ``/proc/meminfo`` file provides information about the total number of persistent hugetlb pages in the kernel's huge page pool." "``/proc/sys/vm/nr_hugepages`` indicates the current number of "persistent" huge pages in the kernel's huge page pool." "The administrator may shrink the pool of persistent huge pages for the default huge page size by setting the ``nr_hugepages`` sysctl to a smaller value." So, the documentation implies that these interfaces should display the number of persistent hugetlb pages. As you have discovered, all but the sysctl interface (and /proc/sys/vm/nr_hugepages) displays the total number of hugetlb pages rather than the number of persistent hugetlb pages. If we wanted to match the documentation, it seems we should change all the "show" interfaces to display persistent huge pages. However, I am a bit concerned about how this may impact end users. There are two types if inconsistencies in these interfaces. 1) As this patch points out, not all "show" interfaces provide the same information. sysctl (/proc/sys/vm/nr_hugepages) displays the number of persistent hugetlb pages, while the others display the total number of hugetlb pages. 2) The show/read interfaces generally provide the total number of hugetlb pages, and the update/write interfaces update the number of persistent hugetlb pages. Both of these situations can lead to user confusion. My 'guess' is that this has not been a widespread issue as most hugetlb users do not configure overcommit/surplus hugetlb pages and thus total number of hugetlb pages is the same as number of persistent hugetlb pages. Right now, I would suggest making all these interfaces display/take the number of persistent hugetlb pages for consistency. This also matches the documentation. Thoughts? -- Mike Kravetz > > Signed-off-by: Xueshi Hu > --- > mm/hugetlb.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index e327a5a7602c..76af189053f0 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -4606,7 +4606,7 @@ static int hugetlb_sysctl_handler_common(bool obey_mempolicy, > void *buffer, size_t *length, loff_t *ppos) > { > struct hstate *h = &default_hstate; > - unsigned long tmp = h->max_huge_pages; > + unsigned long tmp = h->nr_huge_pages; > int ret; > > if (!hugepages_supported()) > -- > 2.40.1 > >