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From: Chris Mason <clm@fb.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: "linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"jlayton@kernel.org" <jlayton@kernel.org>,
	"hch@infradead.org" <hch@infradead.org>
Subject: Re: [RFC 0/8] Replacing the readpages a_op
Date: Mon, 13 Jan 2020 18:00:52 +0000	[thread overview]
Message-ID: <15C84CC9-3196-441D-94DE-F3FD7AC364F0@fb.com> (raw)
In-Reply-To: <20200113174008.GB332@bombadil.infradead.org>

On 13 Jan 2020, at 12:40, Matthew Wilcox wrote:

> On Mon, Jan 13, 2020 at 04:42:10PM +0000, Chris Mason wrote:
>
> I did do a couple of helpers for lists for iomap before deciding the
> whole thing was too painful.  I didn't look at btrfs until just now, 
> but, um ...
>
> int extent_readpages(struct address_space *mapping, struct list_head 
> *pages,
>                      unsigned nr_pages)
> ..
>         struct page *pagepool[16];
> ..
>         while (!list_empty(pages)) {
> ..
>                         list_del(&page->lru);
>                         if (add_to_page_cache_lru(page, mapping, 
> page->index,
> ..
>                         pagepool[nr++] = page;
>
> you're basically doing exactly what i'm proposing to be the new 
> interface!
> OK, you get one extra page per batch ;-P

This is true, I didn't explain that part well ;)  Depending on 
compression etc we might end up poking the xarray inside the actual IO 
functions, but the main difference is that btrfs is building a single 
bio.  You're moving the plug so you'll merge into single bio, but I'd 
rather build 2MB bios than merge them.

I guess it doesn't feel like enough of a win to justify the churn.  If 
we find a way to do much larger pagevecs, I think this makes more sense.

-chris


  reply	other threads:[~2020-01-13 18:01 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-13 15:37 [RFC 0/8] Replacing the readpages a_op Matthew Wilcox
2020-01-13 15:37 ` [PATCH 1/8] pagevec: Add an iterator Matthew Wilcox
2020-01-13 15:37 ` [PATCH 2/8] mm: Fix the return type of __do_page_cache_readahead Matthew Wilcox
2020-01-13 15:37 ` [PATCH 3/8] mm: Use a pagevec for readahead Matthew Wilcox
2020-01-13 15:37 ` [PATCH 4/8] mm/fs: Add a_ops->readahead Matthew Wilcox
2020-01-13 18:22   ` Daniel Wagner
2020-01-13 19:17     ` Matthew Wilcox
2020-01-13 15:37 ` [PATCH 5/8] iomap,xfs: Convert from readpages to readahead Matthew Wilcox
2020-01-13 15:37 ` [PATCH 6/8] cifs: " Matthew Wilcox
2020-01-13 15:37 ` [PATCH 7/8] mm: Remove add_to_page_cache_locked Matthew Wilcox
2020-01-13 15:37 ` [PATCH 8/8] mm: Unify all add_to_page_cache variants Matthew Wilcox
2020-01-13 16:42 ` [RFC 0/8] Replacing the readpages a_op Chris Mason
2020-01-13 17:40   ` Matthew Wilcox
2020-01-13 18:00     ` Chris Mason [this message]
2020-01-13 21:58       ` Matthew Wilcox
2020-01-13 22:00         ` Jens Axboe
2020-01-13 22:10           ` Matthew Wilcox
2020-01-13 22:14             ` Jens Axboe
2020-01-13 22:27               ` Matthew Wilcox
2020-01-13 22:30                 ` Jens Axboe
2020-01-13 22:34                 ` Chris Mason
2020-01-14  1:01                   ` Matthew Wilcox
2020-01-14  1:07                     ` Chris Mason
2020-01-13 17:54   ` Matthew Wilcox
2020-01-13 22:19     ` Jens Axboe

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