On 11/12/2020 15:38, Johannes Weiner wrote:

On Fri, Dec 11, 2020 at 02:20:11PM +0000, Pavel Begunkov wrote:

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On 11/12/2020 14:06, Johannes Weiner wrote:

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On Wed, Dec 09, 2020 at 08:40:05AM +0000, Christoph Hellwig wrote:

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+	/*
+	 * 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".

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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