From: Oleg Nesterov <oleg@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Michal Hocko <mhocko@suse.com>,
Kirill Shutemov <kirill@shutemov.name>,
Jann Horn <jannh@google.com>, Kirill Tkhai <ktkhai@virtuozzo.com>,
Hugh Dickins <hughd@google.com>,
Leon Romanovsky <leonro@nvidia.com>, Jan Kara <jack@suse.cz>,
John Hubbard <jhubbard@nvidia.com>,
Christoph Hellwig <hch@lst.de>,
Andrew Morton <akpm@linux-foundation.org>,
Jason Gunthorpe <jgg@ziepe.ca>,
Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 4/5] mm: Do early cow for pinned pages during fork() for ptes
Date: Tue, 22 Sep 2020 14:40:14 +0200 [thread overview]
Message-ID: <20200922124013.GD11679@redhat.com> (raw)
In-Reply-To: <20200922114839.GC11679@redhat.com>
On 09/22, Oleg Nesterov wrote:
>
> On 09/21, Peter Xu wrote:
> >
> > @@ -859,6 +989,25 @@ static int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> > spin_needbreak(src_ptl) || spin_needbreak(dst_ptl))
> > break;
> > }
> > +
> > + if (unlikely(data.cow_new_page)) {
> > + /*
> > + * If cow_new_page set, we must be at the 2nd round of
> > + * a previous COPY_MM_BREAK_COW. Try to arm the new
> > + * page now. Note that in all cases page_break_cow()
> > + * will properly release the objects in copy_mm_data.
> > + */
> > + WARN_ON_ONCE(copy_ret != COPY_MM_BREAK_COW);
> > + if (pte_install_copied_page(dst_mm, new, src_pte,
> > + dst_pte, addr, rss,
> > + &data)) {
> > + /* We installed the pte successfully; move on */
> > + progress++;
> > + continue;
>
> I'm afraid I misread this patch too ;)
>
> But it seems to me in this case the main loop can really "leak"
> COPY_MM_BREAK_COW. Suppose the the next 31 pte's are pte_none() and
> need_resched() is true.
>
> No?
If yes, perhaps we can simplify the copy_ret/cow_new_page logic and make
it more explicit?
Something like below, on top of this patch...
Oleg.
--- x/mm/memory.c
+++ x/mm/memory.c
@@ -704,17 +704,6 @@
};
};
-static inline void page_release_cow(struct copy_mm_data *data)
-{
- /* The old page should only be released in page_duplicate() */
- WARN_ON_ONCE(data->cow_old_page);
-
- if (data->cow_new_page) {
- put_page(data->cow_new_page);
- data->cow_new_page = NULL;
- }
-}
-
/*
* Duplicate the page for this PTE. Returns zero if page copied (so we need to
* retry on the same PTE again to arm the copied page very soon), or negative
@@ -925,7 +914,7 @@
if (!pte_same(*src_pte, data->cow_oldpte)) {
/* PTE has changed under us. Release the page and retry */
- page_release_cow(data);
+ put_page(data->cow_new_page);
return false;
}
@@ -936,12 +925,6 @@
set_pte_at(dst_mm, addr, dst_pte, entry);
rss[mm_counter(new_page)]++;
- /*
- * Manually clear the new page pointer since we've moved ownership to
- * the newly armed PTE.
- */
- data->cow_new_page = NULL;
-
return true;
}
@@ -958,16 +941,12 @@
struct copy_mm_data data;
again:
- /* We don't reset this for COPY_MM_BREAK_COW */
- memset(&data, 0, sizeof(data));
-
-again_break_cow:
init_rss_vec(rss);
dst_pte = pte_alloc_map_lock(dst_mm, dst_pmd, addr, &dst_ptl);
if (!dst_pte) {
- /* Guarantee that the new page is released if there is */
- page_release_cow(&data);
+ if (unlikely(copy_ret == COPY_MM_BREAK_COW))
+ put_page(data.cow_new_page);
return -ENOMEM;
}
src_pte = pte_offset_map(src_pmd, addr);
@@ -978,6 +957,22 @@
arch_enter_lazy_mmu_mode();
progress = 0;
+ if (unlikely(copy_ret == COPY_MM_BREAK_COW)) {
+ /*
+ * Note that in all cases pte_install_copied_page()
+ * will properly release the objects in copy_mm_data.
+ */
+ copy_ret = COPY_MM_DONE;
+ if (pte_install_copied_page(dst_mm, new, src_pte,
+ dst_pte, addr, rss,
+ &data)) {
+ /* We installed the pte successfully; move on */
+ progress++;
+ goto next;
+ }
+ /* PTE changed. Retry this pte (falls through) */
+ }
+
do {
/*
* We are holding two locks at this point - either of them
@@ -990,24 +985,6 @@
break;
}
- if (unlikely(data.cow_new_page)) {
- /*
- * If cow_new_page set, we must be at the 2nd round of
- * a previous COPY_MM_BREAK_COW. Try to arm the new
- * page now. Note that in all cases page_break_cow()
- * will properly release the objects in copy_mm_data.
- */
- WARN_ON_ONCE(copy_ret != COPY_MM_BREAK_COW);
- if (pte_install_copied_page(dst_mm, new, src_pte,
- dst_pte, addr, rss,
- &data)) {
- /* We installed the pte successfully; move on */
- progress++;
- continue;
- }
- /* PTE changed. Retry this pte (falls through) */
- }
-
if (pte_none(*src_pte)) {
progress++;
continue;
@@ -1017,6 +994,7 @@
if (copy_ret != COPY_MM_DONE)
break;
progress += 8;
+next:
} while (dst_pte++, src_pte++, addr += PAGE_SIZE, addr != end);
arch_leave_lazy_mmu_mode();
@@ -1030,13 +1008,14 @@
case COPY_MM_SWAP_CONT:
if (add_swap_count_continuation(data.entry, GFP_KERNEL) < 0)
return -ENOMEM;
- break;
+ copy_ret = COPY_MM_DONE;
+ goto again;
case COPY_MM_BREAK_COW:
/* Do accounting onto parent mm directly */
ret = page_duplicate(src_mm, vma, addr, &data);
if (ret)
return ret;
- goto again_break_cow;
+ goto again;
case COPY_MM_DONE:
/* This means we're all good. */
break;
next prev parent reply other threads:[~2020-09-22 12:40 UTC|newest]
Thread overview: 110+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-21 21:17 [PATCH 0/5] mm: Break COW for pinned pages during fork() Peter Xu
2020-09-21 21:17 ` [PATCH 1/5] mm: Introduce mm_struct.has_pinned Peter Xu
2020-09-21 21:43 ` Jann Horn
2020-09-21 22:30 ` Peter Xu
2020-09-21 22:47 ` Jann Horn
2020-09-22 11:54 ` Jason Gunthorpe
2020-09-22 14:28 ` Peter Xu
2020-09-22 15:56 ` Jason Gunthorpe
2020-09-22 16:25 ` Linus Torvalds
2020-09-21 23:53 ` John Hubbard
2020-09-22 0:01 ` John Hubbard
2020-09-22 15:17 ` Peter Xu
2020-09-22 16:10 ` Jason Gunthorpe
2020-09-22 17:54 ` Peter Xu
2020-09-22 19:11 ` Jason Gunthorpe
2020-09-23 0:27 ` Peter Xu
2020-09-23 13:10 ` Peter Xu
2020-09-23 14:20 ` Jan Kara
2020-09-23 17:12 ` Jason Gunthorpe
2020-09-24 7:44 ` Jan Kara
2020-09-24 14:02 ` Jason Gunthorpe
2020-09-24 14:45 ` Jan Kara
2020-09-23 17:07 ` Jason Gunthorpe
2020-09-24 14:35 ` Peter Xu
2020-09-24 16:51 ` Jason Gunthorpe
2020-09-24 17:55 ` Peter Xu
2020-09-24 18:15 ` Jason Gunthorpe
2020-09-24 18:34 ` Peter Xu
2020-09-24 18:39 ` Jason Gunthorpe
2020-09-24 21:30 ` Peter Xu
2020-09-25 19:56 ` Linus Torvalds
2020-09-25 21:06 ` Linus Torvalds
2020-09-26 0:41 ` Jason Gunthorpe
2020-09-26 1:15 ` Linus Torvalds
2020-09-26 22:28 ` Linus Torvalds
2020-09-27 6:23 ` Leon Romanovsky
2020-09-27 18:16 ` Linus Torvalds
2020-09-27 18:45 ` Linus Torvalds
2020-09-28 12:49 ` Jason Gunthorpe
2020-09-28 16:17 ` Linus Torvalds
2020-09-28 17:22 ` Peter Xu
2020-09-28 17:54 ` Linus Torvalds
2020-09-28 18:39 ` Jason Gunthorpe
2020-09-28 19:29 ` Linus Torvalds
2020-09-28 23:57 ` Jason Gunthorpe
2020-09-29 0:18 ` John Hubbard
2020-09-28 19:36 ` Linus Torvalds
2020-09-28 19:50 ` Linus Torvalds
2020-09-28 22:51 ` Jason Gunthorpe
2020-09-29 0:30 ` Peter Xu
2020-10-08 5:49 ` Leon Romanovsky
2020-09-28 17:13 ` Peter Xu
2020-09-25 21:13 ` Peter Xu
2020-09-25 22:08 ` Linus Torvalds
2020-09-22 18:02 ` John Hubbard
2020-09-22 18:15 ` Peter Xu
2020-09-22 19:11 ` John Hubbard
2020-09-27 0:41 ` [mm] 698ac7610f: will-it-scale.per_thread_ops 8.2% improvement kernel test robot
2020-09-21 21:17 ` [PATCH 2/5] mm/fork: Pass new vma pointer into copy_page_range() Peter Xu
2020-09-21 21:17 ` [PATCH 3/5] mm: Rework return value for copy_one_pte() Peter Xu
2020-09-22 7:11 ` John Hubbard
2020-09-22 15:29 ` Peter Xu
2020-09-22 10:08 ` Oleg Nesterov
2020-09-22 10:18 ` Oleg Nesterov
2020-09-22 15:36 ` Peter Xu
2020-09-22 15:48 ` Oleg Nesterov
2020-09-22 16:03 ` Peter Xu
2020-09-22 16:53 ` Oleg Nesterov
2020-09-22 18:13 ` Peter Xu
2020-09-22 18:23 ` Oleg Nesterov
2020-09-22 18:49 ` Peter Xu
2020-09-23 6:52 ` Oleg Nesterov
2020-09-23 17:16 ` Linus Torvalds
2020-09-23 21:24 ` Linus Torvalds
2020-09-21 21:20 ` [PATCH 4/5] mm: Do early cow for pinned pages during fork() for ptes Peter Xu
2020-09-21 21:55 ` Jann Horn
2020-09-21 22:18 ` John Hubbard
2020-09-21 22:27 ` Jann Horn
2020-09-22 0:08 ` John Hubbard
2020-09-21 22:27 ` Peter Xu
2020-09-22 11:48 ` Oleg Nesterov
2020-09-22 12:40 ` Oleg Nesterov [this message]
2020-09-22 15:58 ` Peter Xu
2020-09-22 16:52 ` Oleg Nesterov
2020-09-22 18:34 ` Peter Xu
2020-09-22 18:44 ` Oleg Nesterov
2020-09-23 1:03 ` Peter Xu
2020-09-23 20:25 ` Linus Torvalds
2020-09-24 15:08 ` Peter Xu
2020-09-24 11:48 ` Kirill Tkhai
2020-09-24 15:16 ` Peter Xu
2020-09-21 21:20 ` [PATCH 5/5] mm/thp: Split huge pmds/puds if they're pinned when fork() Peter Xu
2020-09-22 6:41 ` John Hubbard
2020-09-22 10:33 ` Jan Kara
2020-09-22 20:01 ` John Hubbard
2020-09-23 9:22 ` Jan Kara
2020-09-23 13:50 ` Peter Xu
2020-09-23 14:01 ` Jan Kara
2020-09-23 15:44 ` Peter Xu
2020-09-23 20:19 ` John Hubbard
2020-09-24 18:49 ` Peter Xu
2020-09-23 16:06 ` Peter Xu
2020-09-22 12:05 ` Jason Gunthorpe
2020-09-23 15:24 ` Peter Xu
2020-09-23 16:07 ` Yang Shi
2020-09-24 15:47 ` Peter Xu
2020-09-24 17:29 ` Yang Shi
2020-09-23 17:17 ` Jason Gunthorpe
2020-09-23 10:21 ` [PATCH 0/5] mm: Break COW for pinned pages during fork() Leon Romanovsky
2020-09-23 15:37 ` Peter Xu
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