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Date: Tue, 5 Jan 2021 21:34:33 +0000 From: Matthew Wilcox <willy@...radead.org> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Hugh Dickins <hughd@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, syzbot <syzbot+2fc0712f8f8b8b8fa0ef@...kaller.appspotmail.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, syzkaller-bugs <syzkaller-bugs@...glegroups.com> Subject: Re: kernel BUG at mm/page-writeback.c:LINE! On Tue, Jan 05, 2021 at 01:22:49PM -0800, Linus Torvalds wrote: > On Tue, Jan 5, 2021 at 1:13 PM Hugh Dickins <hughd@...gle.com> wrote: > > > > I was going to raise a question, whether you should now revert > > 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and BUG_ON(PageWriteback)"): > > which would not have gone in like that if c2407cf7d22d were already in. > > Honestly, even if it wasn't for that PageTail issue, I think > 073861ed77b6 is just the right thing to do anyway. It just feels _so_ > much safer to not have the possibility of that page wait thing > following while the page is possibly then being free'd and re-used at > the same time. > > So I think the only reason to revert that commit would be if we were > to find that it's a huge performance problem to raise the page > refcount temporarily. Which I think is very unlikely (since we already > dirty the page structure due to the page flags modification - although > they are far enough apart that it might be a different cacheline). struct pages _tend_ to be 64 bytes on 64-bit platforms (and i suspect you're long past caring about performance on 32-bit platforms).
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