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[172.125.77.130]) by smtp.gmail.com with ESMTPSA id p22sm2175853oth.38.2021.02.05.19.01.49 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 05 Feb 2021 19:01:50 -0800 (PST) From: Bakul Shah Message-Id: <0076DB2B-48BC-45D3-8278-3D8528431E87@iitbombay.org> Content-Type: multipart/alternative; boundary="Apple-Mail=_BBAFA7AD-51DF-4914-93B1-89E00374577F" Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.60.0.2.21\)) Date: Fri, 5 Feb 2021 19:01:48 -0800 In-Reply-To: To: Dan Cross References: <20210205003315.GK13701@mcvoy.com> <26D923CF-5319-4207-BA28-6EFA0E3BB1F8@iitbombay.org> <20210205141820.GO13701@mcvoy.com> <0253BE0F-94CB-41BB-921D-6BD09A188601@iitbombay.org> X-Mailer: Apple Mail (2.3654.60.0.2.21) Subject: Re: [TUHS] FreeBSD behind the times? (was: Favorite unix design principles?) X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: TUHS main list Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" --Apple-Mail=_BBAFA7AD-51DF-4914-93B1-89E00374577F Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii > On Feb 5, 2021, at 6:06 PM, Dan Cross wrote: >=20 > On Fri, Feb 5, 2021 at 7:04 PM Bakul Shah > wrote: >=20 > And you can keep track of mapped pages and read/write from them if > necessary even if you have a separate cache for any compressed = pages. >=20 > In essence you pass the ownership of a page's data from a compressed > page cache to the mapped page. Just like in processor cache coherence > algorithms there is one source of truth: the current owner of a cached > unit (line or page or whatever). In other words, the you see via = mmap(2) > will be the exact same page you will see via read(2). Not having = actually > tried this I may have missed corner cases + any practical = considerations > complicating things but *conceptually* this doesn't seem hard. >=20 > In essence, that's what the merged page/buffer cache is all about: = file IO (read/write) operations are satisfied from the same memory cache = that backs up VM objects. I agree that conceptually it's not that = complex; but that's not what ZFS does. Good that we agree on that at least! This is why it would be good to = hear from Bonwick/Moore. --Apple-Mail=_BBAFA7AD-51DF-4914-93B1-89E00374577F Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=us-ascii

On Feb 5, 2021, at 6:06 PM, Dan Cross <crossd@gmail.com> = wrote:

On Fri, = Feb 5, 2021 at 7:04 PM Bakul Shah <bakul@iitbombay.org>= wrote:

  =   And you can = keep track of mapped pages and read/write from them if
    necessary even if you have = a  separate cache for any compressed pages.

In essence you pass the ownership of a page's data from a = compressed
page cache to the mapped page. Just like in = processor cache coherence
algorithms there is one source = of truth: the current owner of a cached
unit (line or page = or whatever). In other words, the you see via mmap(2)
will = be the exact same page you will see via read(2). Not having actually
tried this I may have missed corner cases + any practical = considerations
complicating things but *conceptually* this = doesn't seem hard.

In essence, that's what the merged page/buffer cache is all = about: file IO (read/write) operations are satisfied from the same = memory cache that backs up VM objects. I agree that conceptually it's = not that complex; but that's not what ZFS = does.

Good = that we agree on that at least! This is why it would be good to hear = from Bonwick/Moore.

= --Apple-Mail=_BBAFA7AD-51DF-4914-93B1-89E00374577F--