https://jira.whamcloud.com This file is an XML representation of an issue en-us 9.4.14 940014 05-12-2023 https://jira.whamcloud.com/browse/LU-2825 Lustre <p>Looking at struct cl_page there seems to be a lot of wasted memory, and since there may be millions of these structures in memory for every client, this wasted space can be considerable.</p> <ul class="alternate" type="square"> <li>32-bit cp_ref is followed by 64-bit cp_obj, wastes 4 bytes</li> <li>32-bit cp_state is followed by 64-bit cp_batch, wastes 4 bytes</li> <li>cp_state only has 5 states, could fit into a 3-bit field</li> <li>cp_type only has 1 bit, could fit into a 1-bit field, and is immutable after creation so no worries about racy updates/locking</li> <li>32-bit cp_flags is followed by 64-bit cp_sync_io, wastes 4 bytes</li> <li>cp_flags only has 1 bit, could fit into a 1-bit field (not totally sure about locking)</li> <li>64-bit cp_task is only set in 2 places, and never used</li> <li>64-bit cp_queue_ref and cp_obj_ref are only used under USE_LU_REF and can also be made conditional</li> </ul> <p>The structure cl_req has similar space wastage, though it isn't used as often as cl_page:</p> <ul class="alternate" type="square"> <li>32-bit crq_type is followed by 64-bit crq_pages, wastes 4 bytes</li> <li>crq_type only uses two flags, could be a bitfield</li> <li>32-bit crq_npages is followed by 64-bi crq_o, wastes 4 bytes</li> <li>32-bit crq_nrobjs is followed by 64-bit crq_layers, wastes 4 bytes</li> </ul> <p>Using the "pahole" program (part of the "dwarves" package) can report on binary structures for space wastage and alignment problems.</p> LU-2825

shrink cl_page structure size

Improvement Major Closed Won't Fix Jinshan Xiong Andreas Dilger patch Mon, 18 Feb 2013 02:45:20 +0000 Thu, 8 Feb 2018 18:17:42 +0000 Thu, 8 Feb 2018 18:17:42 +0000 Lustre 2.4.0 0 4 <p>Hi Andreas,</p> <p>I have opened a review request for this here -&gt; <a href="http://review.whamcloud.com/#/c/7210/" class="external-link" target="_blank" rel="nofollow noopener">http://review.whamcloud.com/#/c/7210/</a><br/> I have made the following changes:</p> <p>cl_page:<br/> 1) changed the position of cp_ref, cp_state, cp_flags and cp_type to better suit the alignment.<br/> 2) Converted cp_flags and cp_type members to bitfields of sizes 1 and 2 bits respectively.<br/> 3) Could not change cp_state to a bitfield since we access its address at one place.<br/> This leads to a saving of 16 bytes. </p> <p>cl_req:<br/> 1) changed the position of crq_nrpages for better alignment.<br/> 2) converted crq_type to a bitfield of 2 bits.<br/> This leads to a saving of 8 bytes.</p> <p>close old tickets</p> Development Rank 1|hzvjan: Rank (Obsolete) 6841