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Fri, 11 Sep 2020 05:56:31 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id AC8BCAB8B; Fri, 11 Sep 2020 09:56:45 +0000 (UTC) Subject: Re: [PATCH 02/17] btrfs: calculate inline extent buffer page size based on page size To: Qu Wenruo , linux-btrfs@vger.kernel.org References: <20200908075230.86856-1-wqu@suse.com> <20200908075230.86856-3-wqu@suse.com> From: Nikolay Borisov Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= xsFNBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/nSSP8YgfwoOqwrP+JR4pIqRK0AWWeWCSwmZ T7g+RbfPFlmQp+EwFWOtABXlKC54zgSf+uulGwx5JAUFVUIRBmnHOYi/lUiE0yhpnb1KCA7f u/W+DkwGerXqhhe9TvQoGwgCKNfzFPZoM+gZrm+kWv03QLUCr210n4cwaCPJ0Nr9Z3c582xc bCUVbsjt7BN0CFa2BByulrx5xD9sDAYIqfLCcZetAqsTRGxM7LD0kh5WlKzOeAXj5r8DOrU2 GdZS33uKZI/kZJZVytSmZpswDsKhnGzRN1BANGP8sC+WD4eRXajOmNh2HL4P+meO1TlM3GLl EQd2shHFY0qjEo7wxKZI1RyZZ5AgJnSmehrPCyuIyVY210CbMaIKHUIsTqRgY5GaNME24w7h TyyVCy2qAM8fLJ4Vw5bycM/u5xfWm7gyTb9V1TkZ3o1MTrEsrcqFiRrBY94Rs0oQkZvunqia c+NprYSaOG1Cta14o94eMH271Kka/reEwSZkC7T+o9hZ4zi2CcLcY0DXj0qdId7vUKSJjEep c++s8ncFekh1MPhkOgNj8pk17OAESanmDwksmzh1j12lgA5lTFPrJeRNu6/isC2zyZhTwMWs k3LkcTa8ZXxh0RfWAqgx/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABzSJOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuZGU+wsF4BBMBAgAiBQJYijkSAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAAKCRBxvoJG5T8oV/B6D/9a8EcRPdHg8uLEPywuJR8URwXzkofT5bZE IfGF0Z+Lt2ADe+nLOXrwKsamhweUFAvwEUxxnndovRLPOpWerTOAl47lxad08080jXnGfYFS Dc+ew7C3SFI4tFFHln8Y22Q9075saZ2yQS1ywJy+TFPADIprAZXnPbbbNbGtJLoq0LTiESnD w/SUC6sfikYwGRS94Dc9qO4nWyEvBK3Ql8NkoY0Sjky3B0vL572Gq0ytILDDGYuZVo4alUs8 LeXS5ukoZIw1QYXVstDJQnYjFxYgoQ5uGVi4t7FsFM/6ykYDzbIPNOx49Rbh9W4uKsLVhTzG BDTzdvX4ARl9La2kCQIjjWRg+XGuBM5rxT/NaTS78PXjhqWNYlGc5OhO0l8e5DIS2tXwYMDY LuHYNkkpMFksBslldvNttSNei7xr5VwjVqW4vASk2Aak5AleXZS+xIq2FADPS/XSgIaepyTV tkfnyreep1pk09cjfXY4A7qpEFwazCRZg9LLvYVc2M2eFQHDMtXsH59nOMstXx2OtNMcx5p8 0a5FHXE/HoXz3p9bD0uIUq6p04VYOHsMasHqHPbsMAq9V2OCytJQPWwe46bBjYZCOwG0+x58 fBFreP/NiJNeTQPOa6FoxLOLXMuVtpbcXIqKQDoEte9aMpoj9L24f60G4q+pL/54ql2VRscK d87BTQRYigc+ARAAyJSq9EFk28++SLfg791xOh28tLI6Yr8wwEOvM3wKeTfTZd+caVb9gBBy wxYhIopKlK1zq2YP7ZjTP1aPJGoWvcQZ8fVFdK/1nW+Z8/NTjaOx1mfrrtTGtFxVBdSCgqBB jHTnlDYV1R5plJqK+ggEP1a0mr/rpQ9dFGvgf/5jkVpRnH6BY0aYFPprRL8ZCcdv2DeeicOO YMobD5g7g/poQzHLLeT0+y1qiLIFefNABLN06Lf0GBZC5l8hCM3Rpb4ObyQ4B9PmL/KTn2FV Xq/c0scGMdXD2QeWLePC+yLMhf1fZby1vVJ59pXGq+o7XXfYA7xX0JsTUNxVPx/MgK8aLjYW hX+TRA4bCr4uYt/S3ThDRywSX6Hr1lyp4FJBwgyb8iv42it8KvoeOsHqVbuCIGRCXqGGiaeX Wa0M/oxN1vJjMSIEVzBAPi16tztL/wQtFHJtZAdCnuzFAz8ue6GzvsyBj97pzkBVacwp3/Mw qbiu7sDz7yB0d7J2tFBJYNpVt/Lce6nQhrvon0VqiWeMHxgtQ4k92Eja9u80JDaKnHDdjdwq FUikZirB28UiLPQV6PvCckgIiukmz/5ctAfKpyYRGfez+JbAGl6iCvHYt/wAZ7Oqe/3Cirs5 KhaXBcMmJR1qo8QH8eYZ+qhFE3bSPH446+5oEw8A9v5oonKV7zMAEQEAAcLBXwQYAQIACQUC WIoHPgIbDAAKCRBxvoJG5T8oV1pyD/4zdXdOL0lhkSIjJWGqz7Idvo0wjVHSSQCbOwZDWNTN JBTP0BUxHpPu/Z8gRNNP9/k6i63T4eL1xjy4umTwJaej1X15H8Hsh+zakADyWHadbjcUXCkg OJK4NsfqhMuaIYIHbToi9K5pAKnV953xTrK6oYVyd/Rmkmb+wgsbYQJ0Ur1Ficwhp6qU1CaJ mJwFjaWaVgUERoxcejL4ruds66LM9Z1Qqgoer62ZneID6ovmzpCWbi2sfbz98+kW46aA/w8r 7sulgs1KXWhBSv5aWqKU8C4twKjlV2XsztUUsyrjHFj91j31pnHRklBgXHTD/pSRsN0UvM26 lPs0g3ryVlG5wiZ9+JbI3sKMfbdfdOeLxtL25ujs443rw1s/PVghphoeadVAKMPINeRCgoJH zZV/2Z/myWPRWWl/79amy/9MfxffZqO9rfugRBORY0ywPHLDdo9Kmzoxoxp9w3uTrTLZaT9M KIuxEcV8wcVjr+Wr9zRl06waOCkgrQbTPp631hToxo+4rA1jiQF2M80HAet65ytBVR2pFGZF zGYYLqiG+mpUZ+FPjxk9kpkRYz61mTLSY7tuFljExfJWMGfgSg1OxfLV631jV1TcdUnx+h3l Sqs2vMhAVt14zT8mpIuu2VNxcontxgVr1kzYA/tQg32fVRbGr449j1gw57BV9i0vww== Message-ID: <9bc8bd10-dc66-3215-1ef2-b5df3cd00883@suse.com> Date: Fri, 11 Sep 2020 12:56:29 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200908075230.86856-3-wqu@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 8.09.20 г. 10:52 ч., Qu Wenruo wrote: > Btrfs only support 64K as max node size, thus for 4K page system, we > would have at most 16 pages for one extent buffer. > > But for 64K system, we only need and always need one page for extent > buffer. -EAMBIGIOUS. It should be "For a system using 64k pages we would really have have just a single page" > This stays true even for future subpage sized sector size support (as > long as extent buffer doesn't cross 64K boundary). > > So this patch will change how INLINE_EXTENT_BUFFER_PAGES is calculated. > > Instead of using fixed 16 pages, use (64K / PAGE_SIZE) as the result. > This should save some bytes for extent buffer structure for 64K > systems. I'd rephrase the whole changelog as something along the lines of : "Currently btrfs hardcodes the number of inline pages it uses to 16 which in turn has an effect on MAX_INLINE_EXTENT_BUFFER_SIZE effectively defining the upper limit of the size of extent buffer. For systems using 4k pages this works out fine but on 64k page systems this results in unnecessary memory overhead. That's due to the fact BTRFS_MAX_METADATA_BLOCKSIZE is defined as 64k so having INLINE_EXTENT_BUFFER_PAGES set to 16 on a 64k system results in extent_buffer::pages being unnecessarily large since an eb can be mapped with just a single page but the pages array would be 16 entries large. Fix this by changing the way we calculate the size of the pages array by exploiting the fact an eb can't be larger than 64k so choosing enough pages to fit it" > > Signed-off-by: Qu Wenruo This patch must be split into 2: 1. Changing the defines 2. Simplifying num_extent_pages > --- > fs/btrfs/extent_io.h | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h > index 00a88f2eb5ab..e16c5449ba48 100644 > --- a/fs/btrfs/extent_io.h > +++ b/fs/btrfs/extent_io.h > @@ -86,8 +86,8 @@ struct extent_io_ops { > }; > > > -#define INLINE_EXTENT_BUFFER_PAGES 16 > -#define MAX_INLINE_EXTENT_BUFFER_SIZE (INLINE_EXTENT_BUFFER_PAGES * PAGE_SIZE) > +#define MAX_INLINE_EXTENT_BUFFER_SIZE SZ_64K > +#define INLINE_EXTENT_BUFFER_PAGES (MAX_INLINE_EXTENT_BUFFER_SIZE / PAGE_SIZE) Actually having the defines like that it makes no sense to keep MAX_INLINE_EXTENT_BUFFER_SIZE around since it has the same value as BTRFS_MAX_METADATA_BLOCKSIZE. So why not just remove MAX_INLINE_EXTENT_BUFFER_SIZE and use BTRFS_MAX_METADATA_BLOCKSIZE when calculating INLINE_EXTENT_BUFFER_PAGES. > struct extent_buffer { > u64 start; > unsigned long len; > @@ -227,8 +227,15 @@ void wait_on_extent_buffer_writeback(struct extent_buffer *eb); > > static inline int num_extent_pages(const struct extent_buffer *eb) > { > - return (round_up(eb->start + eb->len, PAGE_SIZE) >> PAGE_SHIFT) - > - (eb->start >> PAGE_SHIFT); > + /* > + * For sectorsize == PAGE_SIZE case, since eb is always aligned to > + * sectorsize, it's just (eb->len / PAGE_SIZE) >> PAGE_SHIFT. > + * > + * For sectorsize < PAGE_SIZE case, we only want to support 64K > + * PAGE_SIZE, and ensured all tree blocks won't cross page boundary. > + * So in that case we always got 1 page. > + */ > + return (round_up(eb->len, PAGE_SIZE) >> PAGE_SHIFT); > } > > static inline int extent_buffer_uptodate(const struct extent_buffer *eb) >