linux-kernel - Re: [PATCH v9 03/10] mm/rmap: Split try_to_munlock from try_to

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Date:   Tue, 25 May 2021 16:45:28 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Liam Howlett <liam.howlett@...cle.com>
Cc:     Alistair Popple <apopple@...dia.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        "bskeggs@...hat.com" <bskeggs@...hat.com>,
        "rcampbell@...dia.com" <rcampbell@...dia.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "jhubbard@...dia.com" <jhubbard@...dia.com>,
        "bsingharora@...il.com" <bsingharora@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "jglisse@...hat.com" <jglisse@...hat.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "hughd@...gle.com" <hughd@...gle.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v9 03/10] mm/rmap: Split try_to_munlock from try_to_unmap

On Tue, May 25, 2021 at 11:40 AM Liam Howlett <liam.howlett@...cle.com> wrote:
>
[...]
> >
> > +/*
> > + * Walks the vma's mapping a page and mlocks the page if any locked vma's are
> > + * found. Once one is found the page is locked and the scan can be terminated.
> > + */
>
> Can you please add that this requires the mmap_sem() lock to the
> comments?
>

Why does this require mmap_sem() lock? Also mmap_sem() lock of which mm_struct?

> > +static bool page_mlock_one(struct page *page, struct vm_area_struct *vma,
> > +                              unsigned long address, void *unused)
> > +{
> > +     struct page_vma_mapped_walk pvmw = {
> > +             .page = page,
> > +             .vma = vma,
> > +             .address = address,
> > +     };
> > +
> > +     /* An un-locked vma doesn't have any pages to lock, continue the scan */
> > +     if (!(vma->vm_flags & VM_LOCKED))
> > +             return true;
> > +
> > +     while (page_vma_mapped_walk(&pvmw)) {
> > +             /* PTE-mapped THP are never mlocked */
> > +             if (!PageTransCompound(page))
> > +                     mlock_vma_page(page);
> > +             page_vma_mapped_walk_done(&pvmw);
> > +
> > +             /*
> > +              * no need to continue scanning other vma's if the page has
> > +              * been locked.
> > +              */
> > +             return false;
> > +     }
> > +
> > +     return true;
> > +}