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charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-SPAM-LEVEL: Spam detection results: 0 BAYES_00 -1.9 Bayes spam probability is 0 to 1% DKIM_SIGNED 0.1 Message has a DKIM or DK signature, not necessarily valid DKIM_VALID -0.1 Message has at least one valid DKIM or DK signature DKIM_VALID_AU -0.1 Message has a valid DKIM or DK signature from author's domain DKIM_VALID_EF -0.1 Message has a valid DKIM or DK signature from envelope-from domain DMARC_PASS -0.1 DMARC pass policy FREEMAIL_ENVFROM_END_DIGIT 0.25 Envelope-from freemail username ends in digit FREEMAIL_FROM 0.001 Sender email is commonly abused enduser mail provider RCVD_IN_DNSWL_NONE -0.0001 Sender listed at https://www.dnswl.org/, no trust SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record URIBL_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to URIBL was blocked. See http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block for more information. [proxmox.com] I can't help it, I am sorry in advance, but ... No one is going to bring up the elephant in the room (you may want to call FUSE), such as that backend_write_inode is hit every single time on virtually every memdb_pwrite, i.e. in addition to cfs_fuse_write also on (logically related): cfs_fuse_truncate cfs_fuse_rename cfs_fuse_utimens So these are all separate transactions hitting the backend capturing one and the same event. Additionally, there's nothing atomic about updating __version__ and the actual file ("inode") DB rows, so double the number of transactions hit on every amplified hit yet. Also, locks are persisted into backend only to be removed soon after. WRT to FUSE2 buffering doing just fine for overwrites (<=3D original size), this is true, but then at the same time the mode of PVE operation (albeit quite correctly) is to create a .tmp.XXX (so this is your NEW file being appended) and then rename, whilst all that in-place of that very FUSE mountpoint (not so correctly) and at the same time pmxcfs being completely oblivious to this. I could not help this because this is a developer who - in my opinion - quite rightly wanted to pick the low hanging fruit first with his intuition (and a self-evident reasoning) completely disregarded, however the same scrutiny was not exercised when e.g. bumping limits [1] of that very FS . And that all back then was "tested with touch". And this is all on someone else's codebase that is 10 years old (so designed with different use case in mind, good enough for ~4K files), meanwhile the well-meaning individual even admits he is not a C guru, but is asked to spend a day profiling this multi-threaded CPG bespoke code? NB I will completely leave out what the above mentioned does to the CPG messages flying around, for brevity. But it is why I originally got interested. I am sure I made many friends now that I called even the FUSE migration on its own futile, but well, it is an RFC after all. Thank you, gentlemen. Esi Y On Thu, Sep 19, 2024 at 4:57=E2=80=AFPM Thomas Lamprecht wrote: > > Am 19/09/2024 um 14:45 schrieb Dominik Csapak: > > On 9/19/24 14:01, Thomas Lamprecht wrote: > >> Am 19/09/2024 um 11:52 schrieb Dominik Csapak: > >>> by default libfuse2 limits writes to 4k size, which means that on wri= tes > >>> bigger than that, we do a whole write cycle for each 4k block that co= mes > >>> in. To avoid that, add the option 'big_writes' to allow writes bigger > >>> than 4k at once. > >>> > >>> This should improve pmxcfs performance for situations where we often > >>> write large files (e.g. big ha status) and maybe reduce writes to dis= k. > >> > >> Should? Something like before/after for benchmark numbers, flamegraphs > >> would be really good to have, without those it's rather hard to discus= s > >> this, and I'd like to avoid having to do those, or check the inner wor= kings > >> of the affected fuse userspace/kernel code paths here myself. > > > > well I mean the code change is relatively small and the result is rathe= r clear: > > Well sure the code change is just setting an option... But the actual cha= nge is > abstracted away and would benefit from actually looking into.. > > > in the current case we have the following calls from pmxcfs (shortened = for e-mail) > > when writing a single 128k block: > > (dd if=3D... of=3D/etc/pve/test bs=3D128k count=3D1) > > Better than nothing but still no actual numbers (reduced time, reduced wr= ite amp > in combination with sqlite, ...), some basic analysis over file/write siz= e distribution > on a single node and (e.g. three node) cluster, ... > If that's all obvious for you then great, but as already mentioned in the= past, I > want actual data in commit messages for such stuff, and I cannot really s= ee a downside > of having such numbers. > > Again, as is I'm not really seeing what's to discuss, you send it as RFC = after > all. > > > [...] > > so a factor of 32 less calls to cfs_fuse_write (including memdb_pwrite) > > That can be huge or not so big at all, i.e. as mentioned above, it would = we good to > measure the impact through some other metrics. > > And FWIW, I used bpftrace to count [0] with an unpatched pmxcfs, there I = get > the 32 calls to cfs_fuse_write only for a new file, overwriting the exist= ing > file again with the same amount of data (128k) just causes a single call. > I tried using more data (e.g. from 128k initially to 256k or 512k) and it= 's > always the data divided by 128k (even if the first file has a different s= ize) > > We do not override existing files often, but rather write to a new file a= nd > then rename, but still quite interesting and IMO really showing that just > because this is 1 +-1 line change it doesn't necessarily have to be trivi= al > and obvious in its effects. > > [0]: bpftrace -e 'u:cfs_fuse_write /str(args->path) =3D=3D "/test"/ {@ = =3D count();} END { print(@) }' -p "$(pidof pmxcfs)" > > > >>> If we'd change to libfuse3, this would be a non-issue, since that opt= ion > >>> got removed and is the default there. > >> > >> I'd prefer that. At least if done with the future PVE 9.0, as I do not= think > >> it's a good idea in the middle of a stable release cycle. > > > > why not this change now, and the rewrite to libfuse3 later? that way we= can > > have some improvements now too... > > Because I want some actual data and reasoning first, even if it's quite l= ikely > that this improves things Somehow=E2=84=A2, I'd like to actually know in = what metrics > and by how much (even if just an upper bound due to the benchmark or some > measurement being rather artificial). > > I mean you name the big HA status, why not measure that for real? like, p= robably > among other things, in terms of bytes hitting the block layer, i.e. the a= ctual > backing disk from those requests as then we'd know for real if this can r= educe > the write load there, not just that it maybe should. > > > _______________________________________________ > pve-devel mailing list > pve-devel@lists.proxmox.com > https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel --===============5360423196243984490== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ pve-devel mailing list pve-devel@lists.proxmox.com https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel --===============5360423196243984490==--