linux-kernel - Re: [RFC v2 PATCH] mm: shmem: make stat.st_blksize return huge page size if THP is on

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Date:   Mon, 23 Apr 2018 09:04:35 -0600
From:   Michal Hocko <mhocko@...nel.org>
To:     kirill.shutemov@...ux.intel.com,
        Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     hughd@...gle.com, hch@...radead.org, viro@...iv.linux.org.uk,
        akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 PATCH] mm: shmem: make stat.st_blksize return huge page
 size if THP is on

On Sun 22-04-18 21:28:59, Yang Shi wrote:
> 
> 
> On 4/22/18 6:47 PM, Michal Hocko wrote:
[...]
> > will be used on the first aligned address even when the initial/last
> > portion of the mapping is not THP aligned.
> 
> No, my test shows it is not. And, transhuge_vma_suitable() does check the
> virtual address alignment. If it is not huge page size aligned, it will not
> set PMD for huge page.

It's been quite some time since I've looked at that code but I think you
are wrong. It just doesn't make sense to make the THP decision on the
VMA alignment much. Kirill, can you clarify please?

Please note that I have no objections to actually export the huge page
size as the max block size but your changelog just doesn't make any
sense to me.
-- 
Michal Hocko
SUSE Labs