From: Yang Shi <shy828301@gmail.com> To: Hugh Dickins <hughd@google.com> Cc: Andrew Morton <akpm@linux-foundation.org>, Shakeel Butt <shakeelb@google.com>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Miaohe Lin <linmiaohe@huawei.com>, Mike Kravetz <mike.kravetz@oracle.com>, Michal Hocko <mhocko@suse.com>, Rik van Riel <riel@surriel.com>, Christoph Hellwig <hch@infradead.org>, Matthew Wilcox <willy@infradead.org>, "Eric W. Biederman" <ebiederm@xmission.com>, Alexey Gladkov <legion@kernel.org>, Chris Wilson <chris@chris-wilson.co.uk>, Matthew Auld <matthew.auld@intel.com>, Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-api@vger.kernel.org, Linux MM <linux-mm@kvack.org> Subject: Re: [PATCH 06/16] huge tmpfs: shmem_is_huge(vma, inode, index) Date: Fri, 6 Aug 2021 10:41:49 -0700 [thread overview] Message-ID: <CAHbLzkre9PS_sSo6nQGu5rpsNW=FQ2jvXCMpzmB0OBMT46m87g@mail.gmail.com> (raw) In-Reply-To: <5add2467-3b23-f8b8-e07b-82d8a573ecb7@google.com> On Thu, Aug 5, 2021 at 10:21 PM Hugh Dickins <hughd@google.com> wrote: > > On Wed, 4 Aug 2021, Yang Shi wrote: > > On Wed, Aug 4, 2021 at 1:28 AM Hugh Dickins <hughd@google.com> wrote: > > > > > > Thanks, but despite us agreeing that the race is too unlikely to be worth > > > optimizing against, it does still nag at me ever since you questioned it: > > > silly, but I can't quite be convinced by my own dismissals. > > > > > > I do still want to get rid of SGP_HUGE and SGP_NOHUGE, clearing up those > > > huge allocation decisions remains the intention; but now think to add > > > SGP_NOALLOC for collapse_file() in place of SGP_NOHUGE or SGP_CACHE - > > > to rule out that possibility of mischarge after racing hole-punch, > > > no matter whether it's huge or small. If any such race occurs, > > > collapse_file() should just give up. > > > > > > This being the "Stupid me" SGP_READ idea, except that of course would > > > not work: because half the point of that block in collapse_file() is > > > to initialize the !Uptodate pages, whereas SGP_READ avoids doing so. > > > > > > There is, of course, the danger that in fixing this unlikely mischarge, > > > I've got the code wrong and am introducing a bug: here's what a 17/16 > > > would look like, though it will be better inserted early. I got sick > > > of all the "if (page "s, and was glad of the opportunity to fix that > > > outdated "bring it back from swap" comment - swap got done above. > > > > > > What do you think? Should I add this in or leave it out? > > > > Thanks for keeping investigating this. The patch looks good to me. I > > think we could go this way. Just a nit below. > > Thanks, I'll add it into the series, a patch before SGP_NOHUGE goes away; > but I'm not intending to respin the series until there's more feedback > from others - fcntl versus fadvise is the main issue so far. Thanks, yeah, no hurry to repost. > > > > --- a/include/linux/shmem_fs.h > > > +++ b/include/linux/shmem_fs.h > > > @@ -108,6 +108,7 @@ extern unsigned long shmem_partial_swap_usage(struct address_space *mapping, > > > /* Flag allocation requirements to shmem_getpage */ > > > enum sgp_type { > > > SGP_READ, /* don't exceed i_size, don't allocate page */ > > > + SGP_NOALLOC, /* like SGP_READ, but do use fallocated page */ > > > > The comment looks misleading, it seems SGP_NOALLOC does clear the > > Uptodate flag but SGP_READ doesn't. Or it is fine not to distinguish > > this difference? > > I think you meant to say, SGP_NOALLOC does *set* the Uptodate flag but > SGP_READ doesn't. And a more significant difference, as coded to suit > collapse_file(), is that SGP_NOALLOC returns failure on hole, whereas > SGP_READ returns success: I should have mentioned that. Yes, I mean "set". Sorry for the confusion. > > When I wrote "like SGP_READ" there, I just meant "like what's said in > the line above": would "ditto" be okay with you, and I say > SGP_NOALLOC, /* ditto, but fail on hole, or use fallocated page */ > > I don't really want to get into the "Uptodate" business there. > And I'm afraid someone is going to ask me to write multi-line comments > on each of those SGP_flags, and I'm going to plead "read the source"! OK, I'm fine as is. > > Oh, now I see why you said SGP_NOALLOC does clear the Uptodate flag: > "goto clear", haha: when we clear the page we set the Uptodate flag. > > And I may have another patch to slot in: I was half expecting you to > question why SGP_READ behaves as it does, so in preparing its defence > I checked, and found it was not doing quite what I remembered: changes > were made a long time ago, which have left it slightly suboptimal. > But that really has nothing to do with the rest of this series, > and I don't need to run it past you before reposting. > > I hope that some of the features in this series can be useful to you. Thanks, I will see. > > Thanks, > Hugh
next prev parent reply other threads:[~2021-08-06 17:42 UTC|newest] Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-07-30 7:22 [PATCH 00/16] tmpfs: HUGEPAGE and MEM_LOCK fcntls and memfds Hugh Dickins 2021-07-30 7:25 ` [PATCH 01/16] huge tmpfs: fix fallocate(vanilla) advance over huge pages Hugh Dickins 2021-07-30 21:36 ` Yang Shi 2021-08-01 3:38 ` Hugh Dickins 2021-08-02 20:36 ` Yang Shi 2021-07-30 7:28 ` [PATCH 02/16] huge tmpfs: fix split_huge_page() after FALLOC_FL_KEEP_SIZE Hugh Dickins 2021-07-30 23:48 ` Yang Shi 2021-07-30 7:30 ` [PATCH 03/16] huge tmpfs: remove shrinklist addition from shmem_setattr() Hugh Dickins 2021-07-30 21:50 ` Yang Shi 2021-07-30 7:36 ` [PATCH 04/16] huge tmpfs: revert shmem's use of transhuge_vma_enabled() Hugh Dickins 2021-07-30 21:56 ` Yang Shi 2021-08-01 4:01 ` Hugh Dickins 2021-08-02 20:39 ` Yang Shi 2021-07-30 7:39 ` [PATCH 05/16] huge tmpfs: move shmem_huge_enabled() upwards Hugh Dickins 2021-07-30 21:57 ` Yang Shi 2021-07-30 7:42 ` [PATCH 06/16] huge tmpfs: shmem_is_huge(vma, inode, index) Hugh Dickins 2021-07-30 23:34 ` Yang Shi 2021-08-01 5:22 ` Hugh Dickins 2021-08-01 5:37 ` Hugh Dickins 2021-08-02 21:14 ` Yang Shi 2021-08-04 8:28 ` Hugh Dickins 2021-08-04 19:01 ` Yang Shi 2021-08-06 5:21 ` Hugh Dickins 2021-08-06 17:41 ` Yang Shi [this message] 2021-08-05 23:04 ` Yang Shi 2021-08-06 5:43 ` Hugh Dickins 2021-08-06 17:57 ` Yang Shi 2021-08-12 18:19 ` Yang Shi 2021-07-30 7:45 ` [PATCH 07/16] memfd: memfd_create(name, MFD_HUGEPAGE) for shmem huge pages Hugh Dickins 2021-08-04 14:03 ` Kirill A. Shutemov 2021-08-06 3:33 ` Hugh Dickins 2021-07-30 7:48 ` [PATCH 08/16] huge tmpfs: fcntl(fd, F_HUGEPAGE) and fcntl(fd, F_NOHUGEPAGE) Hugh Dickins 2021-08-04 14:08 ` Kirill A. Shutemov 2021-08-06 4:34 ` Hugh Dickins 2021-07-30 7:51 ` [PATCH 09/16] huge tmpfs: decide stat.st_blksize by shmem_is_huge() Hugh Dickins 2021-07-30 23:40 ` Yang Shi 2021-07-30 7:55 ` [PATCH 10/16] tmpfs: fcntl(fd, F_MEM_LOCK) to memlock a tmpfs file Hugh Dickins 2021-08-03 1:38 ` Matthew Wilcox 2021-08-04 9:15 ` Hugh Dickins 2021-07-30 7:57 ` [PATCH 11/16] tmpfs: fcntl(fd, F_MEM_LOCKED) to test if memlocked Hugh Dickins 2021-07-30 8:00 ` [PATCH 12/16] tmpfs: refuse memlock when fallocated beyond i_size Hugh Dickins 2021-07-30 8:03 ` [PATCH 13/16] mm: bool user_shm_lock(loff_t size, struct ucounts *) Hugh Dickins 2021-07-30 8:06 ` [PATCH 14/16] mm: user_shm_lock(,,getuc) and user_shm_unlock(,,putuc) Hugh Dickins 2021-07-30 8:09 ` [PATCH 15/16] tmpfs: permit changing size of memlocked file Hugh Dickins 2021-07-30 8:13 ` [PATCH 16/16] memfd: memfd_create(name, MFD_MEM_LOCK) for memlocked shmem Hugh Dickins
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='CAHbLzkre9PS_sSo6nQGu5rpsNW=FQ2jvXCMpzmB0OBMT46m87g@mail.gmail.com' \ --to=shy828301@gmail.com \ --cc=akpm@linux-foundation.org \ --cc=chris@chris-wilson.co.uk \ --cc=ebiederm@xmission.com \ --cc=hch@infradead.org \ --cc=hughd@google.com \ --cc=kirill.shutemov@linux.intel.com \ --cc=legion@kernel.org \ --cc=linmiaohe@huawei.com \ --cc=linux-api@vger.kernel.org \ --cc=linux-fsdevel@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-mm@kvack.org \ --cc=matthew.auld@intel.com \ --cc=mhocko@suse.com \ --cc=mike.kravetz@oracle.com \ --cc=riel@surriel.com \ --cc=shakeelb@google.com \ --cc=willy@infradead.org \ --subject='Re: [PATCH 06/16] huge tmpfs: shmem_is_huge(vma, inode, index)' \ /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).