From: Pavel Begunkov <[email protected]>
To: Johannes Weiner <[email protected]>
Cc: Christoph Hellwig <[email protected]>,
Jens Axboe <[email protected]>,
Alexander Viro <[email protected]>,
[email protected], [email protected],
[email protected], [email protected],
Matthew Wilcox <[email protected]>
Subject: Re: [PATCH 2/2] block: no-copy bvec for direct IO
Date: Fri, 11 Dec 2020 15:47:23 +0000 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 11/12/2020 15:38, Johannes Weiner wrote:
> On Fri, Dec 11, 2020 at 02:20:11PM +0000, Pavel Begunkov wrote:
>> On 11/12/2020 14:06, Johannes Weiner wrote:
>>> On Wed, Dec 09, 2020 at 08:40:05AM +0000, Christoph Hellwig wrote:
>>>>> + /*
>>>>> + * In practice groups of pages tend to be accessed/reclaimed/refaulted
>>>>> + * together. To not go over bvec for those who didn't set BIO_WORKINGSET
>>>>> + * approximate it by looking at the first page and inducing it to the
>>>>> + * whole bio
>>>>> + */
>>>>> + if (unlikely(PageWorkingset(iter->bvec->bv_page)))
>>>>> + bio_set_flag(bio, BIO_WORKINGSET);
>>>>
>>>> IIRC the feedback was that we do not need to deal with BIO_WORKINGSET
>>>> at all for direct I/O.
>>>
>>> Yes, this hunk is incorrect. We must not use this flag for direct IO.
>>> It's only for paging IO, when you bring in the data at page->mapping +
>>> page->index. Otherwise you tell the pressure accounting code that you
>>> are paging in a thrashing page, when really you're just reading new
>>> data into a page frame that happens to be hot.
>>>
>>> (As per the other thread, bio_add_page() currently makes that same
>>> mistake for direct IO. I'm fixing that.)
>>
>> I have that stuff fixed, it just didn't go into the RFC. That's basically
>> removing replacing add_page() with its version without BIO_WORKINGSET
I wrote something strange... Should have been "replacing add_page() in
those functions with a version without BIO_WORKINGSET".
>> in bio_iov_iter_get_pages() and all __bio_iov_*_{add,get}_pages() +
>> fix up ./fs/direct-io.c. Should cover all direct cases if I didn't miss
>> some.
>
> Ah, that's fantastic! Thanks for clarifying.
To keep it clear, do we go with what I have stashed (I'm planning to
reiterate this weekend)? or you're going to write it up yourself?
Just in case there is some cooler way you have in mind :)
--
Pavel Begunkov
next prev parent reply other threads:[~2020-12-11 16:50 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-09 2:19 [RFC 0/2] nocopy bvec for direct IO Pavel Begunkov
2020-12-09 2:19 ` [PATCH 1/2] iov: introduce ITER_BVEC_FLAG_FIXED Pavel Begunkov
2020-12-09 8:36 ` Christoph Hellwig
2020-12-09 9:06 ` Christoph Hellwig
2020-12-09 11:54 ` Pavel Begunkov
2020-12-09 13:07 ` Al Viro
2020-12-09 13:37 ` Pavel Begunkov
2020-12-09 17:55 ` Christoph Hellwig
2020-12-09 18:24 ` Matthew Wilcox
2020-12-13 22:09 ` Pavel Begunkov
2020-12-09 2:19 ` [PATCH 2/2] block: no-copy bvec for direct IO Pavel Begunkov
2020-12-09 8:40 ` Christoph Hellwig
2020-12-09 12:01 ` Pavel Begunkov
2020-12-09 12:05 ` Christoph Hellwig
2020-12-09 12:03 ` Pavel Begunkov
2020-12-11 14:06 ` Johannes Weiner
2020-12-11 14:20 ` Pavel Begunkov
2020-12-11 15:38 ` Johannes Weiner
2020-12-11 15:47 ` Pavel Begunkov [this message]
2020-12-11 16:13 ` Johannes Weiner
2020-12-09 21:13 ` David Laight
2020-12-09 6:50 ` [RFC 0/2] nocopy " Christoph Hellwig
2020-12-09 11:54 ` Pavel Begunkov
2020-12-09 16:53 ` Jens Axboe
2020-12-13 22:03 ` Pavel Begunkov
2020-12-09 17:06 ` Al Viro
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