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Date: Fri, 20 Nov 2020 18:39:12 +0800 From: Muchun Song <songmuchun@...edance.com> To: Michal Hocko <mhocko@...e.com> Cc: Jonathan Corbet <corbet@....net>, Mike Kravetz <mike.kravetz@...cle.com>, Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com, dave.hansen@...ux.intel.com, luto@...nel.org, Peter Zijlstra <peterz@...radead.org>, viro@...iv.linux.org.uk, Andrew Morton <akpm@...ux-foundation.org>, paulmck@...nel.org, mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com, Randy Dunlap <rdunlap@...radead.org>, oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de, Mina Almasry <almasrymina@...gle.com>, David Rientjes <rientjes@...gle.com>, Matthew Wilcox <willy@...radead.org>, Oscar Salvador <osalvador@...e.de>, "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>, Xiongchun duan <duanxiongchun@...edance.com>, linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, Linux Memory Management List <linux-mm@...ck.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org> Subject: Re: [External] Re: [PATCH v5 17/21] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap On Fri, Nov 20, 2020 at 4:22 PM Michal Hocko <mhocko@...e.com> wrote: > > On Fri 20-11-20 14:43:21, Muchun Song wrote: > > Add a kernel parameter hugetlb_free_vmemmap to disable the feature of > > freeing unused vmemmap pages associated with each hugetlb page on boot. > > As replied to the config patch. This is fine but I would argue that the > default should be flipped. Saving memory is nice but it comes with > overhead and therefore should be an opt-in. The config option should > only guard compile time dependencies not a user choice. Got it. The default will be flipped in the next version. Thanks. > > > Signed-off-by: Muchun Song <songmuchun@...edance.com> > > --- > > Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++ > > Documentation/admin-guide/mm/hugetlbpage.rst | 3 +++ > > mm/hugetlb_vmemmap.c | 21 +++++++++++++++++++++ > > 3 files changed, 33 insertions(+) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > index 5debfe238027..ccf07293cb63 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -1551,6 +1551,15 @@ > > Documentation/admin-guide/mm/hugetlbpage.rst. > > Format: size[KMG] > > > > + hugetlb_free_vmemmap= > > + [KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, > > + this controls freeing unused vmemmap pages associated > > + with each HugeTLB page. > > + Format: { on (default) | off } > > + > > + on: enable the feature > > + off: disable the feature > > + > > hung_task_panic= > > [KNL] Should the hung task detector generate panics. > > Format: 0 | 1 > > diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst > > index f7b1c7462991..7d6129ee97dd 100644 > > --- a/Documentation/admin-guide/mm/hugetlbpage.rst > > +++ b/Documentation/admin-guide/mm/hugetlbpage.rst > > @@ -145,6 +145,9 @@ default_hugepagesz > > > > will all result in 256 2M huge pages being allocated. Valid default > > huge page size is architecture dependent. > > +hugetlb_free_vmemmap > > + When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this disables freeing > > + unused vmemmap pages associated each HugeTLB page. > > > > When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages`` > > indicates the current number of pre-allocated huge pages of the default size. > > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c > > index 3629165d8158..c958699d1393 100644 > > --- a/mm/hugetlb_vmemmap.c > > +++ b/mm/hugetlb_vmemmap.c > > @@ -144,6 +144,22 @@ static inline bool vmemmap_pmd_huge(pmd_t *pmd) > > } > > #endif > > > > +static bool hugetlb_free_vmemmap_disabled __initdata; > > + > > +static int __init early_hugetlb_free_vmemmap_param(char *buf) > > +{ > > + if (!buf) > > + return -EINVAL; > > + > > + if (!strcmp(buf, "off")) > > + hugetlb_free_vmemmap_disabled = true; > > + else if (strcmp(buf, "on")) > > + return -EINVAL; > > + > > + return 0; > > +} > > +early_param("hugetlb_free_vmemmap", early_hugetlb_free_vmemmap_param); > > + > > static inline unsigned int vmemmap_pages_per_hpage(struct hstate *h) > > { > > return free_vmemmap_pages_per_hpage(h) + RESERVE_VMEMMAP_NR; > > @@ -541,6 +557,11 @@ void __init hugetlb_vmemmap_init(struct hstate *h) > > unsigned int order = huge_page_order(h); > > unsigned int vmemmap_pages; > > > > + if (hugetlb_free_vmemmap_disabled) { > > + pr_info("disable free vmemmap pages for %s\n", h->name); > > + return; > > + } > > + > > vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT; > > /* > > * The head page and the first tail page are not to be freed to buddy > > -- > > 2.11.0 > > -- > Michal Hocko > SUSE Labs -- Yours, Muchun
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