From: Oleg Nesterov <oleg@redhat.com>
To: Song Liu <songliubraving@fb.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux MM <linux-mm@kvack.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"matthew.wilcox@oracle.com" <matthew.wilcox@oracle.com>,
"kirill.shutemov@linux.intel.com"
<kirill.shutemov@linux.intel.com>,
Kernel Team <Kernel-team@fb.com>,
"william.kucharski@oracle.com" <william.kucharski@oracle.com>,
"srikar@linux.vnet.ibm.com" <srikar@linux.vnet.ibm.com>
Subject: Re: [PATCH v12 3/6] mm, thp: introduce FOLL_SPLIT_PMD
Date: Fri, 9 Aug 2019 18:35:52 +0200 [thread overview]
Message-ID: <20190809163551.GB21489@redhat.com> (raw)
In-Reply-To: <48316E06-10B2-439C-AD10-3EC8C86C259C@fb.com>
On 08/08, Song Liu wrote:
>
> > On Aug 8, 2019, at 9:37 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > On 08/07, Song Liu wrote:
> >>
> >> @@ -399,7 +399,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
> >> spin_unlock(ptl);
> >> return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
> >> }
> >> - if (flags & FOLL_SPLIT) {
> >> + if (flags & (FOLL_SPLIT | FOLL_SPLIT_PMD)) {
> >> int ret;
> >> page = pmd_page(*pmd);
> >> if (is_huge_zero_page(page)) {
> >> @@ -408,7 +408,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
> >> split_huge_pmd(vma, pmd, address);
> >> if (pmd_trans_unstable(pmd))
> >> ret = -EBUSY;
> >> - } else {
> >> + } else if (flags & FOLL_SPLIT) {
> >> if (unlikely(!try_get_page(page))) {
> >> spin_unlock(ptl);
> >> return ERR_PTR(-ENOMEM);
> >> @@ -420,6 +420,10 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
> >> put_page(page);
> >> if (pmd_none(*pmd))
> >> return no_page_table(vma, flags);
> >> + } else { /* flags & FOLL_SPLIT_PMD */
> >> + spin_unlock(ptl);
> >> + split_huge_pmd(vma, pmd, address);
> >> + ret = pte_alloc(mm, pmd) ? -ENOMEM : 0;
> >> }
> >
> > Can't resist, let me repeat that I do not like this patch because imo
> > it complicates this code for no reason.
>
> Personally, I don't think this is more complicated than your version.
I do, but of course this is subjective.
> Also, if some code calls follow_pmd_mask() with flags contains both
> FOLL_SPLIT and FOLL_SPLIT_PMD, we should honor FOLL_SPLIT and split the
> huge page.
Heh. why not other way around?
> Of course, there is no code that sets both flags.
and of course, nobody should ever pass both FOLL_SPLIT and FOLL_SPLIT_PMD,
perhaps this deserves a warning.
Not to mention that it would be nice to kill FOLL_SPLIT which has a single
user, but this is another story.
Oleg.
next prev parent reply other threads:[~2019-08-09 16:35 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-07 23:37 [PATCH v12 0/6] THP aware uprobe Song Liu
2019-08-07 23:37 ` [PATCH v12 1/6] mm: move memcmp_pages() and pages_identical() Song Liu
2019-08-07 23:37 ` [PATCH v12 2/6] uprobe: use original page when all uprobes are removed Song Liu
2019-08-07 23:37 ` [PATCH v12 3/6] mm, thp: introduce FOLL_SPLIT_PMD Song Liu
2019-08-08 16:37 ` Oleg Nesterov
2019-08-08 17:16 ` Song Liu
2019-08-09 16:35 ` Oleg Nesterov [this message]
2019-08-09 16:50 ` Song Liu
2019-08-07 23:37 ` [PATCH v12 4/6] uprobe: use FOLL_SPLIT_PMD instead of FOLL_SPLIT Song Liu
2019-08-07 23:37 ` [PATCH v12 5/6] khugepaged: enable collapse pmd for pte-mapped THP Song Liu
2019-08-08 16:33 ` Oleg Nesterov
2019-08-08 17:05 ` Song Liu
2019-08-09 15:24 ` Oleg Nesterov
2019-08-09 16:30 ` Song Liu
2019-08-09 18:01 ` Song Liu
2019-08-12 12:11 ` Kirill A. Shutemov
2019-08-12 13:22 ` Oleg Nesterov
2019-08-12 14:40 ` Kirill A. Shutemov
2019-08-12 21:04 ` Song Liu
2019-08-13 14:44 ` Song Liu
2019-08-15 10:16 ` Oleg Nesterov
2019-08-15 16:27 ` Song Liu
2019-08-13 13:30 ` Oleg Nesterov
2019-08-13 14:05 ` Oleg Nesterov
2019-08-13 15:05 ` Kirill A. Shutemov
2019-08-13 16:24 ` Oleg Nesterov
2019-08-16 14:54 ` Kirill A. Shutemov
2019-08-12 13:06 ` Oleg Nesterov
2019-08-12 14:36 ` Song Liu
2019-08-07 23:37 ` [PATCH v12 6/6] uprobe: collapse THP pmd after removing all uprobes Song Liu
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