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Date: Tue, 26 Sep 2017 13:00:12 +0200 From: Michal Hocko <mhocko@...nel.org> To: Vlastimil Babka <vbabka@...e.cz> Cc: Xishi Qiu <qiuxishi@...wei.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Mel Gorman <mgorman@...hsingularity.net>, Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, zhong jiang <zhongjiang@...wei.com>, yeyunfeng <yeyunfeng@...wei.com>, wanghaitao12@...wei.com, "Zhoukang (A)" <zhoukang7@...wei.com> Subject: Re: [RFC] a question about mlockall() and mprotect() On Tue 26-09-17 11:45:16, Vlastimil Babka wrote: > On 09/26/2017 11:22 AM, Xishi Qiu wrote: > > On 2017/9/26 17:13, Xishi Qiu wrote: > >>> This is still very fuzzy. What are you actually trying to achieve? > >> > >> I don't expect page fault any more after mlock. > >> > > > > Our apps is some thing like RT, and page-fault maybe cause a lot of time, > > e.g. lock, mem reclaim ..., so I use mlock and don't want page fault > > any more. > > Why does your app then have restricted mprotect when calling mlockall() > and only later adjusts the mprotect? Ahh, OK I see what is goging on. So you have PROT_NONE vma at the time mlockall and then later mprotect it something else and want to fault all that memory at the mprotect time? So basically to do --- diff --git a/mm/mprotect.c b/mm/mprotect.c index 6d3e2f082290..b665b5d1c544 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -369,7 +369,7 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev, * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major * fault on access. */ - if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED && + if ((oldflags & (VM_WRITE | VM_LOCKED)) == VM_LOCKED && (newflags & VM_WRITE)) { populate_vma_page_range(vma, start, end, NULL); } -- Michal Hocko SUSE Labs
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