On Thu, Sep 10, 2009 at 07:29:38AM +0800, Theodore Tso wrote: > On Wed, Sep 09, 2009 at 10:51:46PM +0800, Wu Fengguang wrote: > > + * The maximum number of pages to writeout in a single periodic/background > > + * writeback operation. 64MB means I_SYNC may be hold for up to 1 second. > > + * This is not a big problem since we normally do kind of trylock on I_SYNC > > + * for non-data-integrity writes. Userspace tasks doing throttled writeback > > + * do not use this value. > > What's your justification for using 64MB? Where are you getting 1 > second from? On a fast RAID array 64MB can be written in much less > than 1 second. Because this value will be used for desktop and server alike, we have to consider the worst case - for a laptop, it takes about 1 second to write 64MB. It's not accurate to say I_SYNC may be hold for up to 1 second, but the same I_SYNC will be taken, dropped because of congestion, retaken, and this loop could go on for 1 second until a large file have been written 64MB. In the mean while, in the normal case of a single kupdate thread per bdi, that file blocks writeout of other files for 1 second. > More generally, I assume your patches conflict with Jens' per-bdi patches? It is based on latest linux-next tree with the vm.max_writeback_mb patch reverted. The changelog only states the need to increase the size, but not mentioned why it should be made tunable. So I tend to just bump up MAX_WRITEBACK_PAGES. It seems that a large value won't hurt anyone. Or are there demand to further increase it a lot for some server configurations? Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
