linux-kernel - Re: [PATCH v3 1/5] hugetlb: use page.private for hugetlb specific page flags

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Date:   Tue, 26 Jan 2021 09:17:23 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Michal Hocko <mhocko@...nel.org>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 1/5] hugetlb: use page.private for hugetlb specific
 page flags

On Fri, Jan 22, 2021 at 11:52:27AM -0800, Mike Kravetz wrote:
> As hugetlbfs evolved, state information about hugetlb pages was added.
> One 'convenient' way of doing this was to use available fields in tail
> pages.  Over time, it has become difficult to know the meaning or contents
> of fields simply by looking at a small bit of code.  Sometimes, the
> naming is just confusing.  For example: The PagePrivate flag indicates
> a huge page reservation was consumed and needs to be restored if an error
> is encountered and the page is freed before it is instantiated.  The
> page.private field contains the pointer to a subpool if the page is
> associated with one.
> 
> In an effort to make the code more readable, use page.private to contain
> hugetlb specific page flags.  These flags will have test, set and clear
> functions similar to those used for 'normal' page flags.  More importantly,
> an enum of flag values will be created with names that actually reflect
> their purpose.
> 
> In this patch,
> - Create infrastructure for hugetlb specific page flag functions
> - Move subpool pointer to page[1].private to make way for flags
>   Create routines with meaningful names to modify subpool field
> - Use new HPageRestoreReserve flag instead of PagePrivate
> 
> Conversion of other state information will happen in subsequent patches.
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

-- 
Oscar Salvador
SUSE L3