Linux SNPS ARC Archive on lore.kernel.org
 help / color / Atom feed
From: vineetg76@gmail.com (Vineet Gupta)
To: linux-snps-arc@lists.infradead.org
Subject: [PATCH 0/3] eldie generated code for folded p4d/pud
Date: Thu, 10 Oct 2019 13:05:56 -0700
Message-ID: <8ba067a6-8b6a-2414-0f04-b251cd6bb47c@gmail.com> (raw)
In-Reply-To: <20191010085609.xgwkrbzea253wmfg@black.fi.intel.com>


Hi Kirill,

On 10/10/19 1:56 AM, Kirill A. Shutemov wrote:
> On Wed, Oct 09, 2019@10:26:55PM +0000, Vineet Gupta wrote:
>>
>> This series elides extraneous generate code for folded p4d/pud.
>> This came up when trying to remove __ARCH_USE_5LEVEL_HACK from ARC port.
>> The code saving are not a while lot, but still worthwhile IMHO.
> 
> Agreed.

Thx.

So given we are folding pmd too, it seemed we could do the following as well.

+#ifndef __PAGETABLE_PMD_FOLDED
 void pmd_clear_bad(pmd_t *);
+#else
+#define pmd_clear_bad(pmd)        do { } while (0)
+#endif

+#ifndef __PAGETABLE_PMD_FOLDED
 void pmd_clear_bad(pmd_t *pmd)
 {
        pmd_ERROR(*pmd);
        pmd_clear(pmd);
 }
+#endif

I stared at generated code and it seems a bit wrong.
free_pgd_range() -> pgd_none_or_clear_bad() is no longer checking for unmapped pgd
entries as pgd_none/pgd_bad are all stubs returning 0.

This whole pmd folding is a bit confusing considering I only revisit it every few
years :-) Abstraction wise, __PAGETABLE_PMD_FOLDED only has pgd, pte but even in
this regime bunch of pmd macros are still valid

    pmd_set(pmdp, ptep) {
        *pmdp.pud.p4d.pgd = (unsigned long)ptep
    }

Is there a better way to make a mental model of this code folding.

In an ideal world pmd folded would have meant pmd_* routines just vanish - poof.
So in that sense I like your implementation under #[45]LEVEL_HACK where the level
simply vanishes by code like #define p4d_t pgd_t. Perhaps there is lot of historic
baggage, proliferated into arch code so hard to untangle.

Thx,
-Vineet

  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-09 22:26 Vineet.Gupta1
2019-10-09 22:26 ` [PATCH 1/3] asm-generic/tlb: stub out pud_free_tlb() if __PAGETABLE_PUD_FOLDED Vineet.Gupta1
2019-10-09 22:26 ` [PATCH 2/3] asm-generic/tlb: stub out p4d_free_tlb() if __PAGETABLE_P4D_FOLDED Vineet.Gupta1
2019-10-09 22:26 ` [PATCH 3/3] asm-generic/mm: stub out p{4, d}d_clear_bad() if __PAGETABLE_P{4, u}D_FOLDED Vineet.Gupta1
2019-10-10  7:29 ` [PATCH 0/3] eldie generated code for folded p4d/pud peterz
2019-10-10  8:56 ` kirill.shutemov
2019-10-10 20:05   ` vineetg76 [this message]
2019-10-11 12:19     ` kirill
2019-10-11 22:38       ` [RFC] asm-generic/tlb: stub out pmd_free_tlb() if __PAGETABLE_PMD_FOLDED Vineet.Gupta1

Reply instructions:

You may reply publically 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=8ba067a6-8b6a-2414-0f04-b251cd6bb47c@gmail.com \
    --to=vineetg76@gmail.com \
    --cc=linux-snps-arc@lists.infradead.org \
    /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

Linux SNPS ARC Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-snps-arc/0 linux-snps-arc/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-snps-arc linux-snps-arc/ https://lore.kernel.org/linux-snps-arc \
		linux-snps-arc@lists.infradead.org
	public-inbox-index linux-snps-arc

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.infradead.lists.linux-snps-arc


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git