From: Michal Hocko <mhocko@kernel.org>
To: Yang Shi <yang.shi@linux.alibaba.com>
Cc: vbabka@suse.cz, rientjes@google.com, kirill@shutemov.name,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [v2 PATCH] mm: thp: fix false negative of shmem vma's THP eligibility
Date: Tue, 23 Apr 2019 19:52:52 +0200 [thread overview]
Message-ID: <20190423175252.GP25106@dhcp22.suse.cz> (raw)
In-Reply-To: <1556037781-57869-1-git-send-email-yang.shi@linux.alibaba.com>
On Wed 24-04-19 00:43:01, Yang Shi wrote:
> The commit 7635d9cbe832 ("mm, thp, proc: report THP eligibility for each
> vma") introduced THPeligible bit for processes' smaps. But, when checking
> the eligibility for shmem vma, __transparent_hugepage_enabled() is
> called to override the result from shmem_huge_enabled(). It may result
> in the anonymous vma's THP flag override shmem's. For example, running a
> simple test which create THP for shmem, but with anonymous THP disabled,
> when reading the process's smaps, it may show:
>
> 7fc92ec00000-7fc92f000000 rw-s 00000000 00:14 27764 /dev/shm/test
> Size: 4096 kB
> ...
> [snip]
> ...
> ShmemPmdMapped: 4096 kB
> ...
> [snip]
> ...
> THPeligible: 0
>
> And, /proc/meminfo does show THP allocated and PMD mapped too:
>
> ShmemHugePages: 4096 kB
> ShmemPmdMapped: 4096 kB
>
> This doesn't make too much sense. The anonymous THP flag should not
> intervene shmem THP. Calling shmem_huge_enabled() with checking
> MMF_DISABLE_THP sounds good enough. And, we could skip stack and
> dax vma check since we already checked if the vma is shmem already.
Kirill, can we get a confirmation that this is really intended behavior
rather than an omission please? Is this documented? What is a global
knob to simply disable THP system wise?
I have to say that the THP tuning API is one giant mess :/
Btw. this patch also seem to fix khugepaged behavior because it previously
ignored both VM_NOHUGEPAGE and MMF_DISABLE_THP.
> Fixes: 7635d9cbe832 ("mm, thp, proc: report THP eligibility for each vma")
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Kirill A. Shutemov <kirill@shutemov.name>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> ---
> v2: Check VM_NOHUGEPAGE per Michal Hocko
>
> mm/huge_memory.c | 4 ++--
> mm/shmem.c | 3 +++
> 2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 165ea46..5881e82 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -67,8 +67,8 @@ bool transparent_hugepage_enabled(struct vm_area_struct *vma)
> {
> if (vma_is_anonymous(vma))
> return __transparent_hugepage_enabled(vma);
> - if (vma_is_shmem(vma) && shmem_huge_enabled(vma))
> - return __transparent_hugepage_enabled(vma);
> + if (vma_is_shmem(vma))
> + return shmem_huge_enabled(vma);
>
> return false;
> }
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 2275a0f..6f09a31 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -3873,6 +3873,9 @@ bool shmem_huge_enabled(struct vm_area_struct *vma)
> loff_t i_size;
> pgoff_t off;
>
> + if ((vma->vm_flags & VM_NOHUGEPAGE) ||
> + test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
> + return false;
> if (shmem_huge == SHMEM_HUGE_FORCE)
> return true;
> if (shmem_huge == SHMEM_HUGE_DENY)
> --
> 1.8.3.1
>
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-04-23 17:52 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-23 16:43 [v2 PATCH] mm: thp: fix false negative of shmem vma's THP eligibility Yang Shi
2019-04-23 17:52 ` Michal Hocko [this message]
2019-04-23 18:34 ` Yang Shi
2019-04-24 0:22 ` Yang Shi
2019-04-24 7:58 ` Michal Hocko
2019-04-28 19:13 ` Yang Shi
2019-05-06 23:37 ` Yang Shi
2019-05-07 10:47 ` Michal Hocko
2019-05-07 17:10 ` Yang Shi
2019-06-06 18:59 ` Yang Shi
2019-06-07 10:57 ` Hugh Dickins
2019-06-07 14:25 ` Michal Hocko
2019-06-07 18:51 ` Yang Shi
2019-04-24 13:10 ` Vlastimil Babka
2019-04-24 15:47 ` Yang Shi
2019-04-24 16:17 ` Vlastimil Babka
2019-04-25 16:44 ` Yang Shi
2019-06-08 3:58 ` Hugh Dickins
2019-06-10 17:33 ` Yang Shi
2019-06-12 18:44 ` Hugh Dickins
2019-06-12 19:59 ` Yang Shi
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190423175252.GP25106@dhcp22.suse.cz \
--to=mhocko@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=kirill@shutemov.name \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=rientjes@google.com \
--cc=vbabka@suse.cz \
--cc=yang.shi@linux.alibaba.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).