do we really want to export more pdflush details in sysctls
Hi all,
commit fafd688e4c0c34da0f3de909881117d374e4c7af titled "mm: add /proc controls for pdflush threads" adds two more sysctl variables exposing details about pdflush threads. At the same time Jens Axboe is working on the per-bdi writeback patchset which will hopefull soon get rid of the pdflush threads in their current form.
Is it really a good idea to expose more details now or should we revert this patch before 2.6.30 is out?
Cheers,
Christoph
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Quoted 10 lines · Christoph Hellwig
Hi all,
commit
fafd688e4c0c34da0f3de909881117d374e4c7aftitled "mm: add /proc controls for pdflush threads" adds two more sysctl variables exposing details about pdflush threads. At the same time Jens Axboe is working on the per-bdi writeback patchset which will hopefull soon get rid of the pdflush threads in their current form.Is it really a good idea to expose more details now or should we revert this patch before 2.6.30 is out?
Pained me as well when updating the patchset. I see little value in these knobs as it is, I'm imagining that the submitter must have had a use case where it made some difference?
Signature · 7 lines
Jens Axboe -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"[email protected]"> [email protected] </a>
Quoted 9 lines · Jens Axboe
Quoted 8 lines · Christoph Hellwig
Hi all,
commit
fafd688e4c0c34da0f3de909881117d374e4c7aftitled "mm: add /proc controls for pdflush threads" adds two more sysctl variables exposing details about pdflush threads. At the same time Jens Axboe is working on the per-bdi writeback patchset which will hopefull soon get rid of the pdflush threads in their current form.
Quoted 7 lines
Quoted 2 lines
Is it really a good idea to expose more details now or should we revert this patch before 2.6.30 is out?
Pained me as well when updating the patchset. I see little value in these knobs as it is, I'm imagining that the submitter must have had a use case where it made some difference?
No, I didn't. The rational was as explained in the commit log, merely that one size (eg: 2-8 threads) didn't fit all cases, so give the admin a chance at tuning w/o having to recompile.
More importantly, I didn't know that Jens was working on significant changes to writeback. This is sorely needed as from what I see in the code, writeback is very unfair to 'fast' block devices (when both 'fast' and 'slow' devices co-exist), and consequently, the apps that reference them.
Jens: When do you expect to complete the per-bdi patchset?
In any event, it is not a good idea to expose knobs that will soon be obviated so please pull the patch.
Thanks,
-PWM
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Quoted 13 lines · Peter W. Morreale
Quoted 12 lines · Jens Axboe
Quoted 10 lines · Christoph Hellwig
Hi all,
commit
fafd688e4c0c34da0f3de909881117d374e4c7aftitled "mm: add /proc controls for pdflush threads" adds two more sysctl variables exposing details about pdflush threads. At the same time Jens Axboe is working on the per-bdi writeback patchset which will hopefull soon get rid of the pdflush threads in their current form.Is it really a good idea to expose more details now or should we revert this patch before 2.6.30 is out?
Quoted 8 lines
Quoted 4 lines
Pained me as well when updating the patchset. I see little value in these knobs as it is, I'm imagining that the submitter must have had a use case where it made some difference?
No, I didn't. The rational was as explained in the commit log, merely that one size (eg: 2-8 threads) didn't fit all cases, so give the admin a chance at tuning w/o having to recompile.
OK. In general I think it's a pretty bad idea to add such knobs before there are specific use cases, as we have to maintain them forever. I didn't track where this patch came from, I just spotted it in mainline during the merge window.
Quoted 7 lines
More importantly, I didn't know that Jens was working on significant changes to writeback. This is sorely needed as from what I see in the code, writeback is very unfair to 'fast' block devices (when both 'fast' and 'slow' devices co-exist), and consequently, the apps that reference them.
Jens: When do you expect to complete the per-bdi patchset?
Sooner rather than later. I've been working on it the past few days, I needed to make some fundemental changes to support WB_SYNC_ALL and sync(1) properly, unfortunately. I'll be posting an updated patchset early next week.
Quoted 2 lines
In any event, it is not a good idea to expose knobs that will soon be obviated so please pull the patch.
Good, I have reverted the commit in my for-linus branch and will be asking Linus to pull that soonish.
Signature · 7 lines
Jens Axboe -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to [email protected]. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"[email protected]"> [email protected] </a>