Date:   Thu, 9 Feb 2023 01:22:45 +0300
From:   Cyrill Gorcunov <gorcunov@gmail.com>
To:     Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc:     Peter Xu <peterx@redhat.com>, David Hildenbrand <david@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <emmir@google.com>,
        Andrei Vagin <avagin@gmail.com>,
        Danylo Mocherniuk <mdanylo@google.com>,
        Paul Gofman <pgofman@codeweavers.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Shuah Khan <shuah@kernel.org>,
        Christian Brauner <brauner@kernel.org>,
        Yang Shi <shy828301@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Liam R . Howlett" <Liam.Howlett@oracle.com>,
        Yun Zhou <yun.zhou@windriver.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Alex Sierra <alex.sierra@amd.com>,
        Matthew Wilcox <willy@infradead.org>,
        Pasha Tatashin <pasha.tatashin@soleen.com>,
        Mike Rapoport <rppt@kernel.org>, Nadav Amit <namit@vmware.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        "Gustavo A . R . Silva" <gustavoars@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
        Greg KH <gregkh@linuxfoundation.org>, kernel@collabora.com
Subject: Re: [PATCH v10 3/6] fs/proc/task_mmu: Implement IOCTL to get and/or
 the clear info about PTEs
Message-ID: <Y+QgtVSEl4w2NgtJ@grain>
References: <20230202112915.867409-1-usama.anjum@collabora.com>
 <20230202112915.867409-4-usama.anjum@collabora.com>
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On Thu, Feb 02, 2023 at 04:29:12PM +0500, Muhammad Usama Anjum wrote:
...
Hi Muhammad! I'm really sorry for not commenting this code, just out of time and i
fear cant look with precise care at least for some time, hopefully other CRIU guys
pick it up. Anyway, here a few comment from a glance.

> +
> +static inline int pagemap_scan_output(bool wt, bool file, bool pres, bool swap,
> +				      struct pagemap_scan_private *p, unsigned long addr,
> +				      unsigned int len)
> +{

This is a big function and usually it's a flag to not declare it as "inline" until
there very serious reson to.

> +	unsigned long bitmap, cur = PAGEMAP_SCAN_BITMAP(wt, file, pres, swap);
> +	bool cpy = true;
> +	struct page_region *prev = &p->prev;
> +
> +	if (HAS_NO_SPACE(p))
> +		return -ENOSPC;
> +
> +	if (p->max_pages && p->found_pages + len >= p->max_pages)
> +		len = p->max_pages - p->found_pages;
> +	if (!len)
> +		return -EINVAL;
> +
> +	if (p->required_mask)
> +		cpy = ((p->required_mask & cur) == p->required_mask);
> +	if (cpy && p->anyof_mask)
> +		cpy = (p->anyof_mask & cur);
> +	if (cpy && p->excluded_mask)
> +		cpy = !(p->excluded_mask & cur);
> +	bitmap = cur & p->return_mask;
> +	if (cpy && bitmap) {

You can exit early here simply

	if (!cpy || !bitmap)
		return 0;

saving one tab for the code below.

> +		if ((prev->len) && (prev->bitmap == bitmap) &&
> +		    (prev->start + prev->len * PAGE_SIZE == addr)) {
> +			prev->len += len;
> +			p->found_pages += len;
> +		} else if (p->vec_index < p->vec_len) {
> +			if (prev->len) {
> +				memcpy(&p->vec[p->vec_index], prev, sizeof(struct page_region));
> +				p->vec_index++;
> +			}
> +			prev->start = addr;
> +			prev->len = len;
> +			prev->bitmap = bitmap;
> +			p->found_pages += len;
> +		} else {
> +			return -ENOSPC;
> +		}
> +	}
> +	return 0;
> +}
> +
> +static inline int export_prev_to_out(struct pagemap_scan_private *p, struct page_region __user *vec,
> +				     unsigned long *vec_index)
> +{

No need for inline either.

> +	struct page_region *prev = &p->prev;
> +
> +	if (prev->len) {
> +		if (copy_to_user(&vec[*vec_index], prev, sizeof(struct page_region)))
> +			return -EFAULT;
> +		p->vec_index++;
> +		(*vec_index)++;
> +		prev->len = 0;
> +	}
> +	return 0;
> +}
> +
> +static inline int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
> +					 unsigned long end, struct mm_walk *walk)
> +{

Same, no need for inline. I've a few comments more in my mind will try to
collect them tomorrow.