linux-kernel - Re: [PATCH v8 1/3] mm: rearrange madvise code to allow for reuse

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Date:   Sat, 28 Aug 2021 19:19:46 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, ccross@...gle.com,
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        Rob Landley <rob@...dley.net>,
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        Shaohua Li <shli@...ionio.com>,
        Sasha Levin <sasha.levin@...cle.com>,
        Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH v8 1/3] mm: rearrange madvise code to allow for reuse

On Fri, Aug 27, 2021 at 12:18:56PM -0700, Suren Baghdasaryan wrote:
...
>  
> +/*
> + * Apply an madvise behavior to a region of a vma.  madvise_update_vma
> + * will handle splitting a vm area into separate areas, each area with its own
> + * behavior.
> + */
> +static int madvise_vma_behavior(struct vm_area_struct *vma,
> +				struct vm_area_struct **prev,
> +				unsigned long start, unsigned long end,
> +				unsigned long behavior)
> +{
> +	int error = 0;


Hi Suren! A nitpick -- this variable is never used with default value
so I think we could drop assignment here.
...
> +	case MADV_DONTFORK:
> +		new_flags |= VM_DONTCOPY;
> +		break;
> +	case MADV_DOFORK:
> +		if (vma->vm_flags & VM_IO) {
> +			error = -EINVAL;

We can exit early here, without jumping to the end of the function, right?

> +			goto out;
> +		}
> +		new_flags &= ~VM_DONTCOPY;
> +		break;
> +	case MADV_WIPEONFORK:
> +		/* MADV_WIPEONFORK is only supported on anonymous memory. */
> +		if (vma->vm_file || vma->vm_flags & VM_SHARED) {
> +			error = -EINVAL;

And here too.

> +			goto out;
> +		}
> +		new_flags |= VM_WIPEONFORK;
> +		break;
> +	case MADV_KEEPONFORK:
> +		new_flags &= ~VM_WIPEONFORK;
> +		break;
> +	case MADV_DONTDUMP:
> +		new_flags |= VM_DONTDUMP;
> +		break;
> +	case MADV_DODUMP:
> +		if (!is_vm_hugetlb_page(vma) && new_flags & VM_SPECIAL) {
> +			error = -EINVAL;

Same.

> +			goto out;
> +		}
> +		new_flags &= ~VM_DONTDUMP;
> +		break;
> +	case MADV_MERGEABLE:
> +	case MADV_UNMERGEABLE:
> +		error = ksm_madvise(vma, start, end, behavior, &new_flags);
> +		if (error)
> +			goto out;
> +		break;
> +	case MADV_HUGEPAGE:
> +	case MADV_NOHUGEPAGE:
> +		error = hugepage_madvise(vma, &new_flags, behavior);
> +		if (error)
> +			goto out;
> +		break;
> +	}
> +
> +	error = madvise_update_vma(vma, prev, start, end, new_flags);
> +
> +out:

I suppose we better keep the former comment on why we maps ENOMEM to EAGAIN?

	Cyrill