linux-kernel - Re: [PATCH 1/4] of: add struct page support to rmem

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Date:   Mon, 11 Jul 2022 22:51:04 +0800
From:   Li Chen <me@...ux.beauty>
To:     "Arnd Bergmann" <arnd@...db.de>
Cc:     "Catalin Marinas" <catalin.marinas@....com>,
        "Will Deacon" <will@...nel.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Frank Rowand" <frowand.list@...il.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Li Chen" <lchen@...arella.com>,
        "Linux ARM" <linux-arm-kernel@...ts.infradead.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        "DTML" <devicetree@...r.kernel.org>,
        "Linux-MM" <linux-mm@...ck.org>
Subject: Re: [PATCH 1/4] of: add struct page support to rmem

Hi Arnd,

Thanks for your review!
 ---- On Mon, 11 Jul 2022 21:36:12 +0800  Arnd Bergmann <arnd@...db.de> wrote --- 
 > On Mon, Jul 11, 2022 at 2:24 PM Li Chen <me@...ux.beauty> wrote:
 > 
 > > +config OF_RESERVED_MEM_DIO_SUPPORT
 > > +       bool "add Direct I/O support to reserved_mem"
 > > +       depends on ZONE_DEVICE && ARCH_KEEP_MEMBLOCK
 > > +       help
 > > +          By default, reserved memory don't get struct page support, which
 > > +                means you cannot do Direct I/O from this region. This config takes
 > > +                uses of ZONE_DEVICE and treats rmem as hotplug mem to get struct
 > > +                page and DIO support.
 > 
 > This probably does not need to be user visible, it's enough to select it from
 > the drivers that need it.

When you say "user visible", do you mean the config can be dropped or something else like Kconfig type other than bool?

 > 
 > > @@ -72,7 +72,6 @@ void __init fdt_reserved_mem_save_node(unsigned long node, const char *uname,
 > >         rmem->size = size;
 > >
 > >         reserved_mem_count++;
 > > -       return;
 > >  }
 > 
 > This change is not wrong, but it does not belong into the same patch
 > as the rest, just drop it.
 > 
 > > +/**
 > > + * get_reserved_mem_from_dev() - get reserved_mem from a device node
 > > + * @dev: device pointer
 > > + *
 > > + * This function look for reserved_mem from given device.
 > > + *
 > > + * Returns a reserved_mem pointer, or NULL on error.
 > > + */
 > > +struct reserved_mem *get_reserved_mem_from_dev(struct device *dev)
 > > +{
 > > +       struct device_node *np = dev_of_node(dev);
 > > +       struct device_node *rmem_np;
 > > +       struct reserved_mem *rmem = NULL;
 > > +
 > > +       rmem_np = of_parse_phandle(np, "memory-region", 0);
 > > +       if (!rmem_np) {
 > > +               dev_err(dev, "failed to get memory region node\n");
 > > +               return ERR_PTR(-ENODEV);
 > > +       }
 > > +
 > > +       rmem = of_reserved_mem_lookup(rmem_np);
 > > +       if (!rmem) {
 > > +               dev_err(dev, "Failed to lookup reserved memory\n");
 > > +               return ERR_PTR(EINVAL);
 > 
 > This needs to be a negative error code rather than the positive EINVAL.
 > No need to initialize rmem=NULL first if you override it here.
 > 
 > > +       if (likely(reserved_mem_dio_in_region(pfn << PAGE_SHIFT, PAGE_SIZE, rmem) <
 > > +                  0))
 > > +               goto out;
 > 
 > It's not performance critical, so just drop the 'likely()' and put the
 > rest into one line.
 > 
 > 
 > > +       if (page) {
 > > +               *page = pfn_to_page(pfn);
 > > +               get_page(*page);
 > > +       }
 > > +
 > > +       ret = 0;
 > > +
 > > +out:
 > > +       pte_unmap(pte);
 > > +       return ret;
 > > +}
 > 
 > Should you perhaps return an error when 'page' is NULL?
 > 
 > > +#ifdef CONFIG_OF_RESERVED_MEM_DIO_SUPPORT
 > > +int reserved_mem_dio_mmap(struct file *file, struct vm_area_struct *vma, struct reserved_mem *rmem);
 > > +void *reserved_mem_memremap_pages(struct device *dev, struct reserved_mem *rmem);
 > > +#endif
 > 
 > The '#ifdef' check can be dropped here, declarations are normally
 > not hidden like this.
 > 
 >          Arnd
 > 

These will be fixed in v2.

Regards,
Li