linux-kernel - Re: [PATCH -V6 06/21] swap: Support PMD swap mapping when splitting huge PMD

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Message-ID: <87bm7ivoav.fsf@yhuang-dev.intel.com>
Date:   Thu, 25 Oct 2018 08:54:16 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Shaohua Li <shli@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Zi Yan <zi.yan@...rutgers.edu>
Subject: Re: [PATCH -V6 06/21] swap: Support PMD swap mapping when splitting huge PMD

Daniel Jordan <daniel.m.jordan@...cle.com> writes:

> On Wed, Oct 10, 2018 at 03:19:09PM +0800, Huang Ying wrote:
>> +#ifdef CONFIG_THP_SWAP
>> +/*
>> + * The corresponding page table shouldn't be changed under us, that
>> + * is, the page table lock should be held.
>> + */
>> +int split_swap_cluster_map(swp_entry_t entry)
>> +{
>> +	struct swap_info_struct *si;
>> +	struct swap_cluster_info *ci;
>> +	unsigned long offset = swp_offset(entry);
>> +
>> +	VM_BUG_ON(!IS_ALIGNED(offset, SWAPFILE_CLUSTER));
>> +	si = _swap_info_get(entry);
>> +	if (!si)
>> +		return -EBUSY;
>
> I think this return value doesn't get used anywhere?

Yes.  And the error is only possible if page table is corrupted.  So
maybe add a VM_BUG_ON() in it caller __split_huge_swap_pmd()?

Best Regards,
Huang, Ying