linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Mike Rapoport <rppt@kernel.org>
To: Hugh Dickins <hughd@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
	linux-kernel@vger.kernel.org, Alan Cox <alan@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	Christopher Lameter <cl@linux.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Idan Yaniv <idan.yaniv@ibm.com>,
	James Bottomley <jejb@linux.ibm.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Matthew Wilcox <willy@infradead.org>,
	Peter Zijlstra <peterz@infradead.org>,
	"Reshetova, Elena" <elena.reshetova@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tycho Andersen <tycho@tycho.ws>,
	linux-api@vger.kernel.org, linux-mm@kvack.org,
	Mike Rapoport <rppt@linux.ibm.com>
Subject: Re: [RFC PATCH v2 1/5] mm: make HPAGE_PxD_{SHIFT,MASK,SIZE} always available
Date: Tue, 7 Jul 2020 09:47:37 +0300	[thread overview]
Message-ID: <20200707064737.GA9449@kernel.org> (raw)
In-Reply-To: <alpine.LSU.2.11.2007062153000.2793@eggly.anvils>

Hi Hugh,

On Mon, Jul 06, 2020 at 10:07:34PM -0700, Hugh Dickins wrote:
> On Mon, 6 Jul 2020, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@linux.ibm.com>
> > 
> > The definitions of shift, mask and size for the second and the third level
> > of the leaf pages are available only when CONFIG_TRANSPARENT_HUGEPAGE is
> > set. Otherwise they evaluate to BUILD_BUG().
> > 
> > There is no explanation neither in the code nor in the changelog why the
> > usage of, e.g. HPAGE_PMD_SIZE should be only allowed with THP and forbidden
> > otherwise while the definitions of HPAGE_PMD_SIZE and HPAGE_PUD_SIZE
> > express the sizes better than ambiguous HPAGE_SIZE.
> > 
> > Make HPAGE_PxD_{SHIFT,MASK,SIZE} definitions available unconditionally.
> 
> Adding Andrea to Cc, he's the one who structured it that way,
> and should be consulted.
> 
> I'm ambivalent myself.  Many's the time I've been irritated by the
> BUILD_BUG() in HPAGE_etc, and it's responsible for very many #ifdef
> CONFIG_TRANSPARENT_HUGEPAGEs or IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)s
> that you find uglily scattered around the source.
> 
> But that's the point of it: it's warning when you write code peculiar
> to THP, that is going to bloat the build of kernels without any THP.
> 
> So although I've often been tempted to do as you suggest, I've always
> ended up respecting Andrea's intention, and worked around it instead
> (sometimes with #ifdef or IS_ENABLED(), sometimes with
> PMD_{SHIFT,MASK_SIZE}, sometimes with a local definition).

I could do with a local definition as well, but I think HPAGE_PxD_SHIFT
is better and more descriptive than ambiguous HPAGE_SHIFT and I was
thinking about wider change to use "THP" defines rather than "hugetlb"
defines wherever possible. 

In the end, HPAGE_PMD_SIZE does not have to be associated with THP and
limited to it, it just says what is the size of a leaf page at PMD
level.

> Hugh
> 
> > 
> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> > ---
> >  include/linux/huge_mm.h | 10 ++--------
> >  1 file changed, 2 insertions(+), 8 deletions(-)
> > 
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index 71f20776b06c..1f4b44a76e31 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -115,7 +115,6 @@ extern struct kobj_attribute shmem_enabled_attr;
> >  #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
> >  #define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
> >  
> > -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> >  #define HPAGE_PMD_SHIFT PMD_SHIFT
> >  #define HPAGE_PMD_SIZE	((1UL) << HPAGE_PMD_SHIFT)
> >  #define HPAGE_PMD_MASK	(~(HPAGE_PMD_SIZE - 1))
> > @@ -124,6 +123,8 @@ extern struct kobj_attribute shmem_enabled_attr;
> >  #define HPAGE_PUD_SIZE	((1UL) << HPAGE_PUD_SHIFT)
> >  #define HPAGE_PUD_MASK	(~(HPAGE_PUD_SIZE - 1))
> >  
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +
> >  extern unsigned long transparent_hugepage_flags;
> >  
> >  /*
> > @@ -316,13 +317,6 @@ static inline struct list_head *page_deferred_list(struct page *page)
> >  }
> >  
> >  #else /* CONFIG_TRANSPARENT_HUGEPAGE */
> > -#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
> > -#define HPAGE_PMD_MASK ({ BUILD_BUG(); 0; })
> > -#define HPAGE_PMD_SIZE ({ BUILD_BUG(); 0; })
> > -
> > -#define HPAGE_PUD_SHIFT ({ BUILD_BUG(); 0; })
> > -#define HPAGE_PUD_MASK ({ BUILD_BUG(); 0; })
> > -#define HPAGE_PUD_SIZE ({ BUILD_BUG(); 0; })
> >  
> >  static inline int hpage_nr_pages(struct page *page)
> >  {
> > -- 
> > 2.26.2

-- 
Sincerely yours,
Mike.

  reply	other threads:[~2020-07-07  6:47 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-06 17:20 [RFC PATCH v2 0/5] mm: extend memfd with ability to create "secret" memory areas Mike Rapoport
2020-07-06 17:20 ` [RFC PATCH v2 1/5] mm: make HPAGE_PxD_{SHIFT,MASK,SIZE} always available Mike Rapoport
2020-07-07  5:07   ` Hugh Dickins
2020-07-07  6:47     ` Mike Rapoport [this message]
2020-07-10 16:40     ` Andrea Arcangeli
2020-07-10 16:57       ` Matthew Wilcox
2020-07-10 17:08         ` Andrea Arcangeli
2020-07-10 17:12         ` Mike Rapoport
2020-07-06 17:20 ` [RFC PATCH v2 2/5] mmap: make mlock_future_check() global Mike Rapoport
2020-07-06 17:20 ` [RFC PATCH v2 3/5] mm: extend memfd with ability to create "secret" memory areas Mike Rapoport
2020-07-13 10:58   ` Kirill A. Shutemov
2020-07-13 15:31     ` Mike Rapoport
2020-07-06 17:20 ` [RFC PATCH v2 4/5] mm: secretmem: use PMD-size pages to amortize direct map fragmentation Mike Rapoport
2020-07-13 11:05   ` Kirill A. Shutemov
2020-07-13 15:32     ` Mike Rapoport
2020-07-06 17:20 ` [RFC PATCH v2 5/5] mm: secretmem: add ability to reserve memory at boot Mike Rapoport
2020-07-17  8:36 ` [RFC PATCH v2 0/5] mm: extend memfd with ability to create "secret" memory areas Pavel Machek
2020-07-17 14:43   ` James Bottomley

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=20200707064737.GA9449@kernel.org \
    --to=rppt@kernel.org \
    --cc=aarcange@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=alan@linux.intel.com \
    --cc=cl@linux.com \
    --cc=dave.hansen@linux.intel.com \
    --cc=elena.reshetova@intel.com \
    --cc=hughd@google.com \
    --cc=idan.yaniv@ibm.com \
    --cc=jejb@linux.ibm.com \
    --cc=kirill@shutemov.name \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=luto@kernel.org \
    --cc=peterz@infradead.org \
    --cc=rppt@linux.ibm.com \
    --cc=tglx@linutronix.de \
    --cc=tycho@tycho.ws \
    --cc=willy@infradead.org \
    --subject='Re: [RFC PATCH v2 1/5] mm: make HPAGE_PxD_{SHIFT,MASK,SIZE} always available' \
    /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

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).